Showing papers by "University of Nairobi published in 1973"

Cyclical Changes in the Habitat and Climate of an East African Ecosystem

Abstract: Ecological changes in an East African Game Reserve may be attributed to changes in climatic conditions and soil salinity. Tree damage from elephants and overgrazing by livestock are probably secondary factors.

Quadrupedalism in primates

Abstract: Although many primates can be classified as quadrupeds, quadrupedalism in primates has not in the past received as much detailed attention as some other locomotor modes. In the present study quadrupedalism in primates is analysed in terms of positional behavior (locomotor and postural activities in an environmental context) and a number of categories are defined. For arboreal primates different adaptations are evident in animals of different body sizes. However, all adaptations are related to the exploitation of the small branch setting.

Movements and patterns of habitat utilization of elephants in Tsavo National Park, Kenya

Abstract: Summary Following the 1970-71 drought, which resulted in heavy elephant mortality, a long-term study was initiated in Tsavo National Park to determine movements and home ranges of individual elephants and their relations to overall distribution patterns and environmental factors such as rainfall. The preliminary results presented show the post-drought situation but it is recognized that they may not represent normality. Methods used were radio-tracking and observations of visually identifiable individuals. Two aerial counts provided data on overall distribution. Two bulls and two cows were radio-tagged in Tsavo West and two bulls and four cows in Tsavo East, providing home range and movement data. Home ranges in Tsavo West (mean = 350 km2) were considerably smaller than in Tsavo East (mean = 1580 km2). The differences between Tsavo West and Tsavo East are probably related to habitat quality, Tsavo East receiving less rainfall than Tsavo West. This view is supported by the fact that the 1970-71 mortality was largely confined to Tsavo East. The movements of individuals were useful in interpreting relatively major shifts in elephant distribution that occurred within a 4-month period. The following preliminary conclusions emerge from the results obtained so far: (1) Elephants in the Tsavo area, particularly Tsavo East, were more mobile during the study period than was assumed from earlier studies, undertaking long-distance movements in fairly direct response to localized rainfall. (2) A subdivision of the overall population into locally distinct units may exist during the dry season but did not obtain after significant rainfall, when the elephants ranged over wide areas and came into contact with animals from other dry-season units. (3) Circumstantial evidence suggests that food is the primary proximal factor governing movements and distribution of elephants in the area. Food availability, in turn, is determined largely by the spatial and temporal pattern of rainfall.

The effects of environmental temperature on the properties of myofibrillar adenosine triphosphatase from various species of fish.

Abstract: 1. Myofibrillar adenosine triphosphatase (ATPase) activities were measured for white myotomal muscle of 19 species of fish. 2. The activity was measured at different temperatures and after periods of preincubation at 37°C. 3. The inactivation half-life at 37°C depended on environmental temperature, increasing as the temperature increased. 4. Cold-water fish had higher myofibrillar adenosine triphosphatase activity at low temperatures than had warm-water fish. 5. The significance of these results is discussed.

Experimental studies of migration in bugs of the genus Dysdercus.

Abstract: Using a tethered flight technique, migration was studied in the African cotton stainer bugs Dysdercus fasciatus Sign., D. nigrofasciatus Stal, and D. superstitiosus (F.) (Heteroptera: Pyrrhocoridae). The flight system of males of all three species matures in 4-6 days post-eclosion, and flight can continue throughout life. Fed females of D. fasciatus do not fly, but rather histolyse the flight muscles and develop oocytes. Fed females of D. nigrofasciatus and D. superstitiosus exhibit some flight at 4 days post-eclosion, but flight is essentially absent at 6 days when flight muscle histolysis and oogenesis are in progress. Starved females of all three species undertake considerable flight and do not histolyse the flight muscles or develop oocytes. In starved pairs coupling frequency is lowered permitting increased migration. The three species are thus facultative migrants using starvation as a releasing cue. D. fasciatus feeds on baobab (Adansonia) fruits which are seasonally abundant and is the most opportunistic species with the highest reproductive potential and no flight in the presence of food. D. nigrofasciatus feeds on a variety of herbaceous annuals and perennials; it follows an intermediate migration and reproductive strategy. Finally D. superstitiosus is the most catholic in its food habits and has the lowest reproductive potential. Both of the latter species retain some flight capacity even when fed, presumably so that individuals can locate suitable host plants.

African Infant Precocity and Some Social Influences during the First Year

Abstract: In African infants precocious in both mental and motor test performance during the first year of life, environmental factors contributed at least 25% to test score variance. Even in the first year, therefore, social factors must be considered in evaluation of psychological development of these infants.

An experimental study of a plane mixing layer.

Abstract: Examination of existing literature is revealing in that although many investigations have been carried out for a plane mixing layer, only a few present turbulence measurements. It is well-known that both mean velocity and turbulence structure in a plane mixing layer are self-preserving, however there appears to be some variations in these measurements. This investigation presents new data on the mean velocity and the turbulence properties of a plane mixing layer. The turbulence measurements differ by about 25% from those obtained by previous investigators and this is attributed to differences in the experimental set up (i.e., presence or absence of a solid wall in the plane x = 0) and errors associated with hot-wire probes (i.e., longitudinal cooling and thermal wake interference). To avoid difficulties experienced by previous investigators in calculating shear stress distribution from a measured nondimensional mean velocity profile a new method is suggested and this provides good agreement between the calculated and the measured shear stress distribution. ECENTLY, considerable effort has been directed towards the study of free turbulent shear flows. In this group of shear flows a plane, turbulent, incompressible mixing layer between a uniform stream and quiescent surroundings is a com- paratively simple flow to investigate both theoretically and experimentally. However, except for a few investigations (as for example Garshore1; Hackett and Cox2) dealing with mean velocity measurements not much renewed attention appears to have been given to the plane turbulent mixing layer since the appearance of the work of Liepmann and Laufer.3 It should be recalled that Liepmann and Laufer did not measure both the lateral turbulent intensity and the shear stress presumably because is expected to be of the same magnitude as and is expected to be zero. Furthermore, techniques of hot-wire anemometry have developed considerably since their investigation and therefore it is of interest to reinvestigate the plane mixing layer. Since the completion of the present investigation Wygnanski and Fiedler4 have reported extensive and sophisticated turbu- lence measurements in this type of flow. An interesting aspect of their investigation was the geometry of the experimental apparatus. They used a trip wire and a solid wall on the zero velocity side in the plane x = 0. They also used conventional DISA x-wire probes to measure the turbulence parameters and it is now known that the conventional DISA x-wire probes are contaminated by the "thermal cross talk."5 The measurements of Wygnanski and Fiedler are compared with the results of the present investigation obtained with single hot-wires in a plane mixing layer without a solid wall in the plane x = 0. It is anticipated that such a comparison would show up differences, if any, due to the geometry of the experimental apparatus and the probes. Recently Spencer and Jones6 have investigated a general problem of a mixing layer between two parallel streams and as a special case they have reported some data on a plane mixing layer. This information consists of the spreading rate and the mean velocity profile. Although not directly related to the

Reproductive biology of lions (Panthera leo massaica Neumann) in Nairobi National Park

Abstract: Summary This study was conducted from June 1968 to July 1969 and from August 1970 to December 1972 with information available for the intervening period as well as for the first half of 1968, giving records for approximately 5 years. The Nairobi Park lion population has averaged thirty animals with a high percentage (about 60%) of juveniles and a preponderance of females among the adults. Matings occurred all through the year but births showed a distinct peak during December and January. The correlation between number of kills one month and births 3 months later proved statistically significant, suggesting that the level of nutrition may influence fertility. Gestation period is about 110 days; litters, when first seen, averaged three cubs, sex ratio was 1:1. Cubs ioined their pride when 6–8 weeks old, but only if no cubs much older than themselves were present; reasons for this are suggested. Young males left their pride around the age of 2 years and so did most young females, although the latter occasionally stay on with their pride. Youngest age to conceive was about 2| years, intervals between litters averaged 2 years. The hypothesis is put forward that lionesses usually refuse to raise single cubs or those that remain sole survivors at less than 3 months of age. Some evidence to support this thesis is submitted. The reproductive performance of the Nairobi Park lions is compared with those in the Serengeti (Schaller, 1972). The Nairobi population's higher performance despite a higher density there suggests that numbers are still within the optimum. However, this balance is dependent upon a large surplus being able to disperse into the area adjo'ning the Park.2

Levels of Mercury in Urine Correlated with the Use of Skin Lightening Creams

Abstract: The pattern of use of mercury-containing skin lightening creams in a group of young healthy African women was strikingly reflected by the excretion of mercury in urine. Although the levels of mercury in urine frequently associated with manifestations of systemic toxicity were not observed, the mean concentration of mercury in urine, at random sampling, was significantly more than the acceptable upper limit of normal in the group of subjects using mercury-containing skin lightening creams at the time of study. When use of these preparations was discontinued, progressive reduction in mercury concentration in urine Was manifest. Continued use, however, resulted in a variable pattern of subsequent excretion of mercury in urine for which a probable explanation is presented. No definite evidence o of renal damage was obtained, and in particular there were no stigmata of the nephrotic syndrome. The previously published data concerning the association of the nephrotic syndrome with exposure to mercury is reviewed. It is felt that in this respect the subjects of this study constitute a vulnerable population.

Density, distribution, population structure and social organization of the black rhinoceros in Masai Mara Game Reserve

Abstract: Summary Black rhinoceros were studied in the Masai Mara Game Reserve from May 1971 to August 1972. Data were gathered on their density, distribution, population structure, social organization, feeding habits and daily activities. The study area, its vegetation, and the study methods are described briefly. Rhino occupied thirteen separate distribution areas, their distribution being influenced by food availability, water, cover and the presence of human and domestic animals. The number of rhino in each distribution area were within the range of one to thirty-one (densities 0–04 to 0–24/km2), giving a mean density in the rhino-occupied area (749 km2) of 0–14/km2 and in the whole study area (1530 km2) of 0–07/km2. Of the 108 rhino in the population, 73% were adult and 27% were immature. At least one adult and one immature were found in nearly all distribution areas. Adult rhinos formed one age class while the immatures were divided into three age classes. Sex ratio and mortality were investigated. Social units and their home range sizes in relation to density and distribution are discussed. Some aspects of social organization, feeding habits and daily activities will be discussed in a later paper. In conclusion, recommendations for rhino management based on preservation of habitat, particularly cover, more sources of water and human settlement are discussed. Suggestions for further lines of research are also discussed.

The Water Metabolism of a Small East African Antelope: The Dik-Dik

Abstract: 1. In controlled laboratory experiments, rectal temperature, cutaneous moisture evapora­tion, and respiratory rate were studied in the dik-dik. The water balance of the dik-dik was investigated when the antelope were either fully hydrated or dehydrated at the environ­mental temperature of 22 °C or at temperatures alternating between 22 °C and 40 °C at 12 h intervals. 2. Faecal, urinary and evaporative water losses were all reduced by varying degrees during dehydration at 22 °C and 22 to 40 °C. The highest urine osmolality recorded was 4318 ± 105 mosmol/kg H 2 O which occurred when the antelopes were severely dehydrated. 3. At the high air temperatures (40 to 45 °C) cutaneous evaporation measured with a non-ventilated sweat capsule was 19 g H 2 O m -2 h -1 and the respiratory rate over 360/min. Thus the respiratory tract seems to be the major avenue for dissipating excess heat in dik-dik exposed to thermal stress. Injection of adrenaline, intravenously, stimulated sweat dis­charges similar to those observed in the small gazelles, and sheep and goats. 4. The low-water exchange and an efficient kidney helps explain the ability of this small antelope to inhabit hot arid areas.

Reconstruction of the Dental Arcades of Ramapithecus wickeri

Abstract: SPECIES of Ramapithecus are among the few hominoid species currently considered as possibly close to the direct line of human ancestry. One of the most striking resemblances between Ramapithecus and later hominids is the supposed presence of parabolic dental arcades1. In view of the important evolutionary position postulated for these imperfectly known species we have made a reconstruction of the mandible and lower part of the face of the Kenyan species R. wickeri (Leakey)2,3. Previous attempts at reconstruction4–6 have been necessarily conjectural because there were no midline points upon which tooth row divergence could be based. The mandible of R. wickeri (KNM-FT 45)3 is so far the only specimen of this species, or of the closely related R. punjabicus (Pilgrim), that has the midline preserved at any point. It is also likely that it is associated with the maxilla specimen (KNM-FT 46).

Activity Patterns in the Mole-Rats Tachyoryctes Splendens and Heliophobius Argenteocinereus

Abstract: Activity in two unrelated genera of mole-rats, Tachyoryetes and Heliophobius, was studied in the field by recording the movements of animals tagged with radioactive wire. Tachyoryetes shows a single marked activity peak and only leaves its nest between 10.00 and 19.00 hour. Heliophobius shows a more dispersed and prolonged activity pattern although peak activity occurs over approximately the same period as in Tachyoryetes. Heliophobius spends over 50 of the day out of its nest, Tachyoryetes, under 25%.These differences can be attributed to a different function of the nest in the two genera (Tachyoryetes has a multipurpose nest; Heliophobius uses its nest solely for rest), and also to the fact that Tachyoryetes has light-sensitive eyes whereas Heliophobius appears unable to appreciate light; Tachyoryetes periodically comes to the surface to forage and this exposure to light may trigger the 24-hour activity cycle.

Effect of intravenous prolactin infusion on arterial blood pressure in rabbits

Abstract: The effects of intravenous infusions of prolactin on the arterial pressures of decerebrate rabbits were studied. Four groups of animals were used, controls which received saline only and three groups which received prolactin at the rates of 10 |μg/kg/hr, 20 μg/kg/hr and 50 (μg/kg/hour respectively. In the control animals pressure was unchanged after 4 hr. In the 10 [μg/kg/hr group it was 8% above the starting level, in the 20 μg/kg/hr group 19% above and in the 50 [μg/kg/hr group it was 42% above the starting level after 4 hr of infusion.

Energy budget of the lesser flamingo (Phoeniconaias minor Geoifroy)

Abstract: Summary A lesser flamingo's energy surplus, which is defined as the net rate at which it gains chemical energy (averaged over 1 or more whole days) is calculated by estimating the rate at which it filters algae from the water, and then subtracting the energy needed to pump water through the filter, and that expended on general metabolism. From the assumptions made, it follows that a flamingo should be able to make a positive energy surplus if the food concentration exceeds about 0–12 kg dry matter per m3 of water, and if it spends 80% of its time feeding. During incubation, however, less than half the total time can be spent feeding, and in this case the food concentration would need to be at least 0–25 kg/m3. About 2 days would be required to produce an egg at this concentration, and less than 1 day at the highest concentrations observed.

The flamingo and pelican populations of the Rift Valley Lakes in 1968‐69

Abstract: Summary Aerial photographic sample censuses of the flamingoes and pelicans on Lakes Nakuru and Hannington were carried out on four occasions between October 1968 and March 1969. On Lake Nakuru the estimated numbers of flamingoes varied between 172 000 and 401 000, and the pelicans between 6800 and 27 900. There were no pelicans on Lake Hannington, but the number of flamingoes varied between 507 000 and 634 000. It was not possible to distinguish between greater and lesser flamingoes, or between white and pink-backed pelicans on the aerial photographs. On 28–30 March 1969 a census was carried out on twenty-four lakes, between Lake Hannington in the north and the Singida lakes in the south. The total number of flamingoes seen was just over one million, with 22 000 pelicans. About 100 000 lesser flamingo nests were counted from aerial photographs taken over Lake Natron in November 1969.

A comparative study of reproduction in two populations of the insectivorous bats, Otomops martiensseni, at latitudes 1°5′S and 2°30′S

Abstract: The insectivorous bat under review, Otomops martiensseni (Matschie) is essentially an African bat with a distribution from down south to as far north as Kenya. It is cave-dwelling and does not appear to occur in West Africa. In this study, reproduction of two populations, one at Suswa in the Rift Valley, latitude 1°5′S and the other at Ithundu in the Chyulu Hills, latitude 2°30′S was investigated and compared. Regular monthly samples from both populations were collected commencing in March 1970 and running on to February 1972. The bats were processed in the laboratory for pregnancies, weights of testes and foetuses and other measurements and observations. Seasonality in the occurrence of pregnancies was observed in both populations, that is, from October to January only. Also the adult males realized a peak in their mean testicular weight in August, a short period just before the onset of pregnancies thus indicating the most likely time of mating. The female sexual cycle at Ithundu appears to be geared to the rainfall regime as measured at Makindu Meteorological Station about 10 km away. The male sexual cycle, on the other hand, shows a peak in the very dry months suggesting that such a dry spell may be more important than the rain. Molossid bats exhibit variation in their breeding cycles. Summary The breeding cycles of two populations of the cave dwelling insectivorous bat, O. martiensseni have been elucidated. In one population at Ithundu, the adult females show evidence of pregnancies from October to January and the adult males exhibit a peak in their sexual cycle in August. In the Suswa population, a similar state of affairs obtains. In both populations, there is the curious tendency for pregnancies to occur also in May at Suswa and Ithundu; and also in June in Ithundu. But as such pregnancies are not sustained in the ensuing months and are of extremely low magnitude, they cannot be regarded as constituting another breeding season. The peak in the adult male cycle occurred during the dry spell from June to September. The peak in pregnancies at Ithundu appears to coincide with the peak rainfall and it is possible that the same is true of Suswa. Considering that these bats are seasonal in their breeding and that they are only monotocous, their recruitment rate as shown by their age distribution is low.

The structure of a population of mole‐rats, Tachyoryctes splendens, (Rodentia: Rhizomyidae)

Abstract: 803 mole-rats, Tachyoryctes splendens, trapped at Nairobi, Kenya, were used in a population study. Because of their discrete burrow systems and solitary fossorial nature, mark-release methods for population assessment were impracticable and a method was devised using kill-trapped animals. A significantly higher number of adult female than adult male Tachyoryctes were trapped, this however, was found to be due to preferential trapping of females. Tachyoryctes has an average (pre-resorption) litter size of 1.9. The uterine placental scars produced by each litter persist for considerable periods, probably throughout life. It was possible to use the number of placental scars to divide the female population into groups based on the number of litters they had had. Young female mole-rats mature in about 120 days. The average time between successive litters was calculated to be 173 days and it was possible to estimate the age of each female mole-rat from the number of litters she had had. Using this data a life table was constructed. Except for a period of lowered mortality on first attaining sexual maturity, the death rate of the female population was fairly constant, suggesting that fossorial life offers equal protection to all age groups. Tachyoryctes has a low annual rate of recruitment (1.37) which again is probably directly attributable to the protection offered by their fossorial mode of life.

Response of Cowpeas to Salinity and (2-Chloroethyl) trimethyl-ammonium Chloride (CCC)

Abstract: Recent investigations have demonstrated that the growth retardant, (2-chloroethyl) trimethyl-ammonium chloride (CCC) inhibits several aspects of vegetative growth. In solution culture experiments, reduction in plant growth and dry matter production was confirmed in cowpeas, Vigna unguiculata L, (cv. Makueni II), when treated with CCC. The growth retardant had negligible effect on the rate of transpiration per unit leaf area although it slightly increased the relative water content of leaves. Stomatal opening was suppressed by CCC treatment but the number of stomata per unit leaf area was increased by the growth retardant. Variations in mineral element content (K, Ca, N and Na) of shoots are presented and discussed in relation to CCC treatment.

The Kidneys and Urinary Tract

Abstract: The main functions of the kidneys are the regulation of the amount of water and dissolved ions in the body, the excretion of waste matter and the manufacture of erythropoietin, the hormone which regulates red cell synthesis (chapter 4).

The blood coagulation and fibrinolytic enzyme systems in healthy adult Africans and Europeans--a comparative study.

Abstract: In a comparative study of blood coagulation and fibrinolysis in healthy adult East Africans and Europeans, the Europeans were found to have some evidence of a relatively hypercoagulable state, and ...

A comparative study of oocyte development in cotton stainers (dysdercus spp., pyrrhocoridae) and the factors that control egg production

Abstract: The relative importance of three factors - mating, nutrition, and crowding - in regulating the reproductive biology of Dysdercus fasciatus Signoret, D. nigrofasciatus Stal and D. cardinalis Gerst. was studied under standard laboratory conditions. Observations on mated and virgin females of these three species of Dysdercus showed that there were no significant differences in pre-oviposition period and inter-oviposition period. In D. fasciatus and D. nigrofasciatus there was, further, no significant difference in the rate of oocyte development; but D. cardinalis differed from these two species in that mating had a profound effect on the rate of oocyte development and consequently on the first oviposition. However, in all three species of Dysdercus mating had a significant effect on the number of eggs produced in each batch, the egg batches of mated females being significantly larger than those produced by virgin females. Further, in both D. fasciatus and D. nigrofasciatus virgin females lived longer than mated females but in D. nigrofasciatus mating had no significant effect on adult longevity. Mating activity was drastically reduced in starved adult bugs. But where it occurred under these conditions, mating did not have any effect on the development of the oocytes, even in D. cardinalis. Under starvation conditions, growth proceeded up to the stage where yolk deposition would normally occur, then stopped; the oocytes showed no signs of degeneration or oosorption. Crowding of female adults led to the acceleration of oocyte development and the onset of oviposition in all three species. These findings are discussed in relation to the known field biology of the three Dysdercus species. ETUDE COMPAREE DU DEVELOPPEMENT DES OVOCYTES CHEZ LES PUNAISES DU COTON DU GENRE DYSDERCUS (PYRRHOCORIDAE) ET LES FACTEURS QUI CONDITIONNENT LA PRODUCTION D'OEUFS. La biologie de la reproduction de 3 especes de Dysdercus du Kenya a eTE etudiee au laboratoire. Des 3 especes, D. fasciatus Signoret presente Ies periodes les plus courtes de pre-copulation et de pre-oviposition. Puisque cette espece est infeodee a un relativement petit nombre de plantes-hotes, qui ont une courte saison de fructification procurant alors une ample source de nourriture, elle tire un avantage maximum de la brieveTE de cette periode favorable, grâce a la reduction des phases de pre-copulation et de pre-oviposition. Par contre D. nigrofasciatus Stal est adapTEe a un tres grand nombre de plantes hotes et pour elle il n'est pas indispensable d'avoir une tres grande capaciTE de reproduction. Cela s'applique encore mieux a D. cardinalis Gerst. qui a une plus longue periode de pre-copulation et de pre-oviposition. Cette espece prefere les plantes qui sont dispersees sur une grande super***ticie et cela exige une longue periode de vol exploratoire avant de s'alimenter et de se reproduire. Chacune de ces 3 especes s'accouple de facon presque continue, mais les observations faites au laboratoire montrent que l'accouplement n'a aucun effet notable sur la longeviTE des adultes, sur la duree des phases de pre-oviposition ou d'inter-oviposition et sur le nombre total d'œufs pondus chez D. fasciatus et D. nigrofasciatus. Chez D. cardinalis, au contraire, l'accouplement a un effet important sur la vitesse de croissance des ovocytes, mais non sur les autres aspects de la reproduction evoques ci-dessus. Le rassemblement en masse des femelles adultes accelere le developpement des ovocyles et declenche la ponte dans chacune des 3 especes de Dysdercus. L'alimentation a un effet sur le developpement des ovocytes. De jeunes femelles adultes doivent etre alimenTEes pendant au moins 3–4 jours avant de deposer leur premiere ponte. Apres chaque ponte une alimentation plus abondante est encore necessaire pour assurer le maintien de la production d'œufs. Les femelles de chacune des 3 especes peuvent survivre avec de l'eau pure mais leurs ovocytes arretent leur developpement au stade ou normalement se depose le vitellus, mais ils ne sont pas resorbes.

Market structure and industry performance: the case of kenya

Abstract: The pEipsr has two goals. An attempt is made to relate the structural characteristics of industries in Kenya to the performance of industries using the 1963 Census of Industrial Production. Structure is measured by a concentration index, which incorporates the influence of foreign competition, fhile performance is measured by the difference between average price and average cost, as a percentage of average price. Secondly, the paper brings evidence to bear on the controversy over whether the relationship between performance and concentration is continuous and whether concentration alone partly oxpl .ins porformance or whdhnr barriers to entry exert an independent influence on perfor ance in addition to concentration.

East Coast Fever of Cattle: 60Co Irradiation of Infective Particles of Theileria parva

Abstract: SYNOPSIS. Infective particles (IPs) of Theileria parva, the causative organism of East Coast Fever of cattle, were harvested from the tick vector, Rhipicephalus appendiculatus, using an in vitro feeding technic. In a ranging experiment, pairs of cattle were inoculated with aliquots of suspensions of IPs irradiated at doses of 4–137.6 krad. Doses of irradiation in excess of 8 krad appeared to destroy the parasite. In the 2nd and 3rd experiments, groups of 5 cattle were inoculated with aliquots of suspensions containing low and high concentrations of IPs respectively, irradiated at doses of 4–32 krad. In the 2nd experiment, doses of irradiation in excess of 10 krad appeared to destroy the parasite. In the 3rd experiment, at least 1 animal became infected when inoculated with an aliquot of a suspension irradiated at 16 krad. In all experiments, it appeared that increasing doses of irradiation destroyed increasing numbers of IPs. There was no conclusive evidence that IPs which survived irradiation were attenuated, and it appears that vaccination of cattle against ECF is unlikely to be achieved by inoculation of irradiated IPs using the methods described.