Showing papers by "University of Guelph published in 1981"

Ultrastructure, Chemistry, and Function of the Bacterial Wall

Abstract: Publisher Summary This chapter describes the ultrastructure, chemistry and function of the bacterial wall. Cell walls are dynamic and change to fulfill functions dictated by the cell in response to the environment. Most bacteria respond unequivocally to the Gram reaction; that is, some retain the large crystal violet-iodine complex (Gram-positive), whereas others are decolorized by the alcohol treatment (Gram-negative) and can be counterstained. Cell age, autolysin levels, and growth conditions can affect the Gram reaction. Unlike Gram-positive bacteria, freeze-cleaved and -etched Gram-negative cells present a number of cleavage sites within the wall that is an indication of multilayering. This wall is chemically and structurally more complex than its Gram-positive counterpart. Each of the layers of capsule, slime layers, and surface arrays reside above the wall and may be singular or in combination with one another. Each presents unique problems for preservation and visualization by electron microscopy. The chapter also discusses the functional aspects of walls that include (1) interaction with metals; (2) β-lactam drugs and low-level antibiotic resistance; and (3) functional discontinuities in the wall fabric.

The stability of real ecosystems

Abstract: Most current theoretical work on whole ecological communities is based on a conception of community dynamics (see, for example, refs 1, 2) in which the community resides in a neighbourhood of equilibrium. However, there is very little evidence that this is a realistic viewpoint. To test this fundamental assumption ‘empirically’, I have constructed here plausible community matrices1,2 corresponding to 40 real food webs3 and studied their local stability properties. I find that stability (in the sense of tending to return to the presumed equilibrium after a small perturbation) is far more likely if the interaction strengths are chosen in accord with the nature of the particular organisms in each food web, rather than strictly at random. Either this is a monumental coincidence, or the equilibrium viewpoint really is appropriate for quite a few real communities. Additional results of this analysis are that stability generally requires a degree of intraspecific interference on the part of some consumer species, whereas interspecific interference tends to exert a destabilizing influence.

Vitamin D and Its Metabolites in Human and Bovine Milk

Abstract: Human and bovine milk were analyzed for vitamin D, 25-hydroxyvitamin D, 24,25-dihydroxyvitamin D, 25,26-dihydroxyvitamin D and 1,25-dihydroxyvitamin D using exhaustive chromatographic purification procedures coupled with ligand binding assays. Human milk contained the following amounts of antirachitic sterols (pg/ml, mean +/- SD, n = 5): 39 +/- 9 vitamin D; 311 +/- 31 25-hydroxyvitamin D; 52 +/- 8 24,25-hydroxyvitamin D; 32 +/- 9 25,26-dihydroxyvitamin D; 5.1 +/- 0.3 1,25-dihydroxyvitamin D. Normal bovine milk contained levels of these sterols comparable to those found in human milk. Increasing the oral dose of vitamin D to the cows was reflected by an increase of the parent vitamin and 25-hydroxyvitamin D in the milk. Vitamin D-binding protein concentration in human milk whey, determined by Ouchterlony immunodiffusion and radioimmunoassay, was 1--2% of the levels observed in the plasma and was dependent on the stage of lactation. Vitamin D and its metabolites were shown initially to be present in the whey portion but with time migrated into the fat portion of milk. The antirachitic sterols detected account for approximately 25 IU/liter and 27 IU/liter of antirachitic activity in human and bovine milk, respectively. In both species 25-hydroxyvitamin D comprised the majority of the antirachitic sterols detected in normal milk.

Additions and amendments to the classification of reproductive styles in fishes

Abstract: The guild concept is explained to represent peaks in the landscape of reproductive styles, which respond to the ‘altricial ⇄ precocial principle’ caused by the processes of heterochrony and saltation Guilds represent evolutionary trends but not units New evidence for a specialization within the mouthbrooding external bearers is reviewed, eg the unique specialization of juvenile feeding inside the female's buccal cavity Ability to withstand extreme environments is revealed in some water-edge spawners and a new guild of nonguarding aerophils is distinguished The walleye is placed into another guild and the significance of spawning inside of sponges discussed Due to a better understanding of reproductive styles used by some external bearers, termed earlier as forehead, skin and possibly armpit and backpack brooders, a single guild of auxiliary brooders is named The classification of internal bearers is revised into four redefined and renamed guilds — facultative internal bearers, obligate lecithotrophic livebearers, matrotrophous oophages and adephophages, and viviparous trophoderms

A new macrosystem for the phylum Ciliophora doflein, 1901.

Abstract: A new macrosystem for the phylum Ciliophora is described. It is based primarily on the concept of the structural conservatism of the cortical fibrillar structures. Three subphyla, the Postciliodesmatophora, Rhabdophora, and Cyrtophora, are described. These three subphyla are divided respectively into the following classes: (1) the Postciliodesmatophora, into the Karyorelictea and Spirotrichea; (2) Rhabdophora, into the Prostomea and the Litostomea n, nov.; and (3) Cyrtophorea, into the Nassophorea n. nov., Phyllopharyngea, Coipodea, and Oligohymenophorea. The subclass divisions of these eight classes are briefly discussed. Problem areas are indicated where further research will test the relationship proposed by this new macrosystem.

Cellulase and Xylanase Release from Bacteroides succinogenes and Its Importance in the Rumen Environment

Abstract: During growth of Bacteroides succinogenes in a liquid medium with cellulose as the source of carbohydrate, greater than 80% of the carboxymethylcellulase (endo-beta-1,4-glucanase), xylanase, and aryl-beta-xylosidase and 50% of the aryl-beta-glucosidase released from cells into the culture fluid. Less than 25% of the cellobiase activity was detected in the culture fluid. Approximately 50% of each of the released enzymes measured was associated with sedimentable subcellular membrane vesicles. The vesicles appeared to be released from the outer membrane of intact cells by bleb formation, primarily in pockets between the cells and the cellulose, although a few unattached cells with blebs were seen. Many vesicles were seen adhering to cellulose, and they were also seen free in the culture fluid. These data suggest that B. succinogenes releases hydrolytic enzymes in nonsedimentable and particulate forms during growth by a mechanism which has until now received little attention. Cellulose incubated in a porous nylon bag in the rumen was colonized by bacteria resembling B. succinogenes, and subcellular vesicles were seen penetrating channels and fractures in the cellulose. On this basis, it is suggested that B. succinogenes cells in the rumen contribute to an extracellular population of subcellular vesicles that possess cellulolytic and hemicellulolytic activities which probably enhance polymer digestion and provide a source of sugars for microbes lacking polymer-degrading activity, thereby contributing to a stable heterogeneous microbial population.

Saltatory Processes and Altricial to Precocial Forms in the Ontogeny of Fishes

Abstract: SYNOPSIS. Development is not a gradual but a saltatory process. A combination of qualitative changes in form and function—thresholds—creates boundaries between a succession of quantitative intervals—steps. Thresholds can be modified by an altered time of appearance of structures and functions (heterochrony), especially during early ontogeny, to form an operational basis for the prolongation of juvenile characters and adaptability into later ontogeny. Whereas such prolongation enables juvenilization in phylogeny, analogous principles may operate on a much shorter time scale to produce the r -selection-like altricial and the K -selection-like precocial trends in ontogeny. The inherited capacity to adjust constantly to the environment (heterochrony) selects for structural, biochemical and behavioral improvements. The tendency is toward the precocial but the way back to altricial forms is left open. The heterochronous adaptations in early ontogeny can “reverse” the vulnerable specialization, should the environment become less stable and/or the community less competitive. Juvenilization, capable of turning gerontomorphosis into paedomorphosis in evolution, and heterochronous shifts of character anlagen, capable of turning a precocial trend into an altricial trend in ontogeny are both part of the same biological process which operates during early ontogeny.

Numerical simulation of particle trajectories in inhomogeneous turbulence, II: Systems with variable turbulent velocity scale

Abstract: A means of numerical simulation of particle trajectories in inhomogeneous turbulence is described. The method employs a simple coordinate transformation which allows a trajectory in inhomogeneous turbulence to be converted to a corresponding trajectory in homogeneous turbulence. Concentration distributions predicted by the trajectory-simulation method agree precisely with analytical solutions in the special cases of homogeneous turbulence, turbulence with power-law wind and eddy diffusivity profiles, and the neutral atmospheric surface layer.

The organization and evolution of microtubular organelles in ciliated protozoa

Abstract: Summary (1) Ciliated protozoa are viewed as unicellular organisms structured in a hierarchy of organizational levels that include the macromolecular, suborganellar, unit organellar, organellar complex, and organellar system. (2) The ciliate cortex is divided into two major functional regions, the somatic region and the oral region. The fundamental component of the cortex is an organellar complex, the kinetid, whose organizing centre is the kinetosome with which are associated three fibrillar associates diagnostic of ciliates. These three fibrillar associates are the periodically striated kinetodesmal fibril and two microtubular ribbons, the transverse and postciliary ribbons. (3) Somatic and oral kinetids are found to be of three major types: monokinetids are composed of one kinetosome and its fibrillar associates; dikinetids are composed of two kinetosomes and their fibrillar associates; polykinetids are composed of more than two kinetosomes and their fibrillar associptes. (4) The mechanisms underlying kinetid function and development remain largely unexplored. Research into the molecular biology and ultrastructure, especially of mutant forms, should provide basic insights in the near future. (5) The conservation of kinetid structure across major phyla of organisms suggests that this subcellular structure should be useful in phylogenetic analysis despite the concepts of ‘chemical identity’ and ‘organic design’. (6) The evolutionary rate of change of oral features is greater than that of somatic features, probably due to developmental and ecological factors. Nevertheless both cortical regions are constrained by the phenomenon of structural conservatism; that is, the conservation of structure through time is inversely related to the level of biological organization. (7) Eight major groupings of ciliate species are recognized, based on ultrastruc-tural features of the cortex. Several examples of differences between these eight groups and the groups presently recognized are discussed.

Attentional Asymmetries during Concurrent Bimanual Performance

Abstract: An asymmetry of attention was observed when subjects attempted to perform concurrent, relatively independent tasks with the two hands: right-handed subjects performed very much better on a dual task which required them to follow the beat of a metronome with the left while tapping as quickly as they could with the right than with the converse arrangement. It is suggested that attentional strategies which have evolved to allow guidance of interdependent skilled bimanual activities are also used when subjects attempt to perform relatively independent concurrent bimanual movements, which are not observed in the naturally occurring motor repertoire. Thus, interactions between hand, hand preference and nature of task are an important factor in dual task performance.

A kinematic study of long-term habituation to treadmill walking

Abstract: Eighteen young adult male subjects, who were naive to treadmill walking, were walked for two l0 min periods per week on a motorized treadmill for 12 weeks. The subjects were split into three groups with the six subjects in each group walking at a prescribed speed. The relative speeds chosen were 0.55 (slow), 0.86 (normal) and 1.20 (fast) statures/s. The angular and temporal kinematics of gait were analysed in order to study the habituation process. The results show that there is an initial rapid accommodation each time the subjects mount the treadmill. On the first exposure this was followed by a longer and more gradual habituation, However after five 10 min practice sessions this habituation takes place much more rapidly. The results suggest that where measurements are to be made of gait patterns using motorized treadmills, subjects should be previously habituated in distributed practice sessions for about 1 hour, and then not measured within the first 2min of performance.

The effects of soluble salts on the threshold shear velocity of fine sand

Abstract: Wind tunnel tests were carried out to investigate the effects of two soluble salts (NaCl and KCI) on the threshold shear velocity of a well-sorted, fine sand. A sensitive laser monitoring system was used to detect initial grain motion during the tests. Results indicate that even small amounts of soluble salt can significantly increase the threshold velocity of the sand because of cement-like bonds formed between grains that tend to hold individual particles in place. However, with increasing concentration the salt crystal growth causes the initially smooth sand surface to develop an irregular frothy texture which also directly affects the threshold shear velocity. This is indicated by increased scatter of data on the threshold shear velocity-surface salt concentration plots for both NaCl and KCl. Although data scatter is evident, significant exponential relationships do exist between threshold shear velocity and surface salt concentration in each case.

Social Behavior of Microtus pennsylvanicus in Relation to Seasonal Changes in Demography

Abstract: A combined mark-recapture trapping and radiotelemetry study was carried out on a free-ranging population of meadow voles ( Microtus pennsylvanicus ) during summer, fall, and winter. Social relationships of pairs of neighboring voles were determined by examining their spatial and temporal use of areas of overlap. Relationships between social behavior and seasonal changes in population demography were investigated. During summer, reproductively active (RA) males had larger activity areas than RA females, and their areas overlapped substantially with those of both RA males and RA females. RA females had little or no overlap with other RA females. Neither RA males nor RA females used the overlap area with neighbors differently from random expectation. There was little contact between RA voles except when females were in estrus. Then, RA males approached the estrous female and were aggressive towards other RA males. Nonreproductive (NR) voles in summer and fall were more tolerant socially than were RA voles. In winter, activity areas of NR voles overlapped extensively, and these voles shared nests with each other. The composition of the population changed from predominantly RA voles in summer to entirely NR voles in winter.

Ordering of aluminium and silicon in synthetic faujasites

Abstract: The distribution of aluminium and silicon atoms on the tetrahedral sites in synthetic faujasites (zeolites X and Y) has been debated for many years. Although the framework structure of the zeolite is known1, the detailed distribution of Si and Al in the lattice cannot be established by conventional methods, partly because of the very similar scattering powers of silicon and aluminium for X rays and partly because of the difficulties in obtaining crystals of adequate size and perfection. Some inferences have, however, been made on the basis of four indirect approaches: variation of the (cubic) lattice parameter as a function of aluminium content2,3; electrostatic calculations4; change of zeolitic acidity on successive extraction of aluminium from the framework5–7; and the kinetics of crystallization8. All these approaches have assumed the validity of ‘Loewenstein's rule’ which forbids Al atoms from occupying neighbouring tetrahedral sites. High-resolution solid-state 29Si NMR (with magic angle spinning) can determine the detailed Si, Al ordering in zeolites9–16 . NMR coupled with electron diffraction studies has revealed that Loewenstein's rule, generally treated as axiomatic, is broken in Linde A10,13,14 and in at least three other zeolites where Si/Al is nominally unity15. In view of its importance as an archetypal zeolite, particularly commercially, we have re-examined the question of framework ordering in faujasite. We propose new ordering schemes and explain discontinuities in the unit cell constant as a function of composition.

Numerical simulation of particle trajectories in inhomogeneous turbulence, iii: comparison of predictions with experimental data for the atmospheric surface layer

Abstract: It is shown that predictions of a numerical trajectory-simulation method agree closely with the Project Prairie Grass observations of the concentrations 100 m downwind of a continuous point source of sulphur dioxide if the height (z) dependence of the Lagrangian length scale ΛL is chosen as: whereL is the Monin-Obukhov length. The value of 0.5 for ΛL/z in neutral conditions is consistent with the findings of Reid (1979) for the Porton experiment, and is also shown to be the best choice for simulation of an experiment in which concentration profiles were measured a short distance (< 40 m) downwind of an elevated point source of glass beads (40 μn diameter). $$\begin{gathered} \Lambda _L = 0.5z\left( {1 - 6\frac{z}{L}} \right)^{{1 \mathord{\left/ {\vphantom {1 4}} \right. \kern- ulldelimiterspace} 4}} L 0 \hfill \\ \end{gathered} $$

Effect of oxidized fish oil, DL-alpha-tocopheryl acetate and ethoxyquin supplementation on the vitamin E nutrition of rainbow trout (Salmo gairdneri) fed practical diets.

Abstract: A factorial experiment was conducted using two degrees of oxidation of the 7.5% supplemental fish oil (peroxide values of 5 and 120 meq/kg oil), two levels of supplemental DL-apha-tocopheryl acetate (0 and 33 mg/kg diet) and two levels of ethoxyquin (0 and 125 mg/kg diet) supplementation. Dietary thiobarbituric acid number, weight percentage of polyunsaturated fatty acids and omega-three fatty acids in the total fatty acids were significantly (P less than 0.05) different between diets with fresh and highly oxidized oil. Dietary RRR-alpha-tocopherol was significantly (P less than 0.05) reduced by the addition of highly oxidized oil after 24 weeks storage of the feed while supplemental DL-alpha-tocopheryl acetate level was not changed. Fish fed the various diets showed no differences in growth, feed:gain ratio, carcass composition or plasma glutathione peroxidase activity. The mortality, percent red cells hemolyzed by hydrogen peroxide, plasma and liver RRR-alpha-tocopherol concentrations were significantly (P less than 0.05) affected by the addition of highly oxidized oil or DL-alpha-tocopheryl acetate but not by ethoxyquin except that mortality was reduced by supplementary ethoxyquin. The results of this study suggested that no vitamin E or ethoxyquin supplementation was needed to prevent a deficiency of vitamin E in rainbow trout fed a practical diet containing 7.5% of a good quality herring oil for 24 weeks.

The Price-Forecasting Performance of Futures Markets for Live Cattle and Hogs: A Disaggregated Analysis

Abstract: Four hypotheses about the price-forecasting performance of live cattle and hog futures are tested using disaggregated data. Live cattle futures are found to have inadequate forecasting performance for each hypothesis and do not provide better forecasts than lagged cash prices. Live hog futures perform well for three hypotheses, but not when economic conditions are unstable. Hog futures provide better forecasts than lagged cash prices. The analysis does not support the contention that these futures markets are agencies for rational price formation.

Estrogen, Androgen, and Progesterone Biosynthesis by Theca and Granulosa of Preovulatory Follicles in the Pig

Abstract: Prepubertal guts were treated with 1000 IU PMSG and slaughtered at 0, 36, or 72 h, or at 75 h following treatment with 500 JU of hCG at 72 h Theca and granulosa were isolated from preovulatory follicles and cultured for 24 h alone or with FSH or LH and in combination with or without testosterone In vitro accumulation of estradiol-1 7(1 (E2), progesterone (P), testosterone (T), and androstenedione (A) was measured for each culture On a per follicle basis, theca produced E2 in quantities comparable to granulosa, but granulosa required an exogenous aromatizable substrate (T) whereas theca did not Theca was the sole source of androgen, predominantly A, and produced significant quantities of P, though granulosa was the primary producer of P Theca was responsive to LH but not FSH, particularly in the early stages of follicular development, in production of all steroids except E2 The overall thecal production of all steroids increased with development of the follicle to 72 h, and in vivo hCG treatment further stimulated the production of P, A, and T but inhibited E2 biosynthesis In culture in the absence of exogenous steroid, there was a net depletion of A and T by granulosa, matching the accumulation of E2 Granulosa cell androgen content prior to culture was correlated with thecal androgen synthetic activity, providing indirect evidence that thecal androgen is transferred to granulosa cells in vivo In the presence of T, granulosa production of E2 declined with development of the follicle but was enhanced 3 h after hCG treatment in vivo; there was no effect of gonadotropin on in vitro E2 synthesis The granulosa biosynthesis of P increased with follicular development, and was highly responsive to both LH and FSH in the early stages; P production was unaffected by addition of T We conclude that, in the porcine preovulatory follicle, theca is an important source of E2 and the sole source of androgen After transfer from theca to granulosa cells, A is converted to T and thence to E2 Granulosa is also the predominant site of P synthesis

Solubility and sorption of cadmium in soils amended with sewage sludge

Abstract: Summary The mechanisms governing the retention and release of Cd in two soils, a loam and a loamy sand, pretreated with anaerobically digested sewage sludges or with chemical fertilizers, were studied using batch equilibration in 0.05 m Ca(NO3)2 solution containing up to 6 μg Cd/ml. Adsorption rather than precipitation as Cd3(PO4)2 limited solution Cd2+ concentration. With the addition of 50 μg Cd/g, however, precipitation as CdCO3 was likely at pH 7.6. Cadmium adsorption increased with increasing soil pH. The differences in Cd adsorption between different soil treatments were attributed mainly to the soil pH (6.9 to 7.9) induced by sludge application. About 82 to 92 per cent of adsorbed Cd was retained by cation exchange and complexing sites. Soils treated with sludge increased the amount of exchangeable Cd but reduced the amount of complexed Cd compared with the fertilized soil. Cadmium retention by cation exchange became more dominant as the amount of Cd in the soil was increased.

Distribution Patterns of Raptors in Relation to Density of Meadow Voles

Abstract: -Densities of overwintering Red-tailed Hawks (Buteo jamaicensis) and Rough-legged Hawks (Buteo lagopus) were examined in relation to densities of meadow voles (Microtus pennsylvanicus) on six habitat types. Generally, densities of both raptor species were greater in habitats that had higher densities of meadow voles. However, not all habitats with high numbers of voles had high numbers of the raptors. The amount and distribution of cover also appeared to influence the distribution of the raptors. Hence, patches that support high densities of prey may not be profitable foraging sites for predators because other factors may reduce availability of prey. Optimal foraging theory predicts that animals should maximize their net rate of energy intake (Krebs 1973, Pyke et al. 1977). For example, when the food of a predator is distributed unevenly in space, the predator would be expected to spend more time on those patches yielding greatest net gain of energy (MacArthur and Pianka 1966, Krebs 1973, Smith and Sweatman 1974, Zach and Falls 1976a, Pyke et al. 1977, Bobisud and Voxman 1979, Waage 1979). Several studies have shown that predators do concentrate their search efforts in areas of high prey density (Goss-Custard 1970, Simons and Alcock 1971, Smith and Dawkins 1971, Hassel and May 1974, Smith 1974, Smith and Sweatman 1974, Hartwick 1976, Zach and Falls 1976a, b, c). Royama (1970, 1971) hypothesized that predators learn to use the most "profitable" patches where profitable is defined in terms of biomass of prey taken by a predator per unit of hunting time, rather than strictly on the basis of prey density. Few field studies, however, have investigated whether predators concentrate their foraging efforts on the most profitable sites. In the present study, we examined the profitability hypothesis of Royama (1970) by measuring responses of raptors to different densities of meadow voles (Microtus pennsylvanicus). On Toronto International Airport, meadow voles constitute more than 85% of prey items in the diets of overwintering Red-tailed Hawks (Buteo jamaicensis) and Rough-legged Hawks (B. lagopus; Baker 1977). From November to March these hawks devote most of the day to foraging and might be expected to be most numerous in areas where voles are abundant. STUDY AREA AND METHODS Toronto International Airport is on the western perimeter of Metropolitan Toronto, Ontario (79?37'W, 43?41'N). In addition to buildings and paved areas, it includes about 1,200 ha of farmland and assorted grasslands. The airport is surrounded by industrial and urban areas and by flat old-field communities that are largely devoid of trees and shrubs. On the basis of acce s roads and runways, we chose a study area of 827 ha so as to permit a total census of the raptors on the study area. The study area was divided into six habitat types according to vegetation composition and type of land management. Shortgrass habitats (407 ha) were mowed and treated with herbicides regularly by airport personnel so that the average vegetation height was about 10 cm and the dominant plant species was bluegrass (Poa sp.). Agricultural land (273 ha) was classified into four habitat types. Pastures (49 ha) were grazed by cattle except in winter. By early fall, little cover remained on pastures except around clumps of weeds avoided by the cattle. Plowed fields (100 ha) were farmed during summer, then were plowed in early fall and left fallow over winter. Winter wheat (69 ha) was sown in September, and harvested the following July. There was little cover on winter wheat fields over winter. Straw habitats (55 ha) occurred only in 1974-75 when straw from the harvested winter wheat was left in rows in the fields over winter. The straw p ovided good winter cover for voles. Old fields (147 ha) were largely abandoned farm fields (70%) and unmanaged areas near streams and lowlands (30%). They were densely covered by perennial grasses, forbs and hawthorn (Crataegus spp.) seedlings. More detailed description of these habitat types is in Steele (1977). Vole populations were estimated on the basis of livetrapping plots using standard capture/mark/recapture methods (Davis 1956). Estimates were based on the Schnabel (1938) method, using Overton's (1965) modification for known removals. The minimum number of voles known to be alive (MNA) was also tabulated (Krebs 1966). One live-trapping plot was set on each habitat type, with no plot less than 50 m from the habitat boundary, and no plot within 400 m of any other. Each plot was a 0.4-ha grid with one trap set every 10 m for a total of 55 traps per plot. Each plot was trapped every three months and at each sample period the traps

Isolation of an influenza A virus from seals

Abstract: Influenza A virus of serotype Hav1 Neq1 (H7N7 by the 1980 revised influenza typing system proposed by WHO experts) was repeatedly isolated from lung and brain tissues taken from harbor seals (Phoca vitulina) found suffering from pneumonia on Cape Cod Peninsula (U.S.A.) in the winter of 1979–1980. The seal isolates, although of a serotype identical to some fowl plague virus strains, were harmless to chickens and turkeys in transmission experiments. An earlier human infection by a Hav1 Neq1 influenza virus and the serologic relatedness of this avian serotype with the equine 1 serotype are cited in support of the view that influenza viruses with these antigenic characteristics seem to have a facility to pass from birds to mammals.