Showing papers in "Nature in 1965"
TL;DR: In E. coli, the presence of certain group VIIIb transition metal compounds in concentrations of about 1–10 parts per million of the metal in the culture medium causes an inhibition of the cell division process, which implies that the growth process is not markedly affected.
Abstract: IN an investigation of the possible effects of an electric field on growth processes in bacteria, we have discovered a new and interesting effect. In E. coli, the presence of certain group VIIIb transition metal compounds in concentrations of about 1–10 parts per million of the metal in the culture medium causes an inhibition of the cell division process. The bacteria form long filaments, up to 300 times the normal length, which implies that the growth process is not markedly affected.
2,728 citations
TL;DR: In this article, the Burton diphenylamine method was used to estimate extreme sensitivity coupled with a low reagent blank, which was simplified and the blank considerably reduced and the sensitivity increased.
Abstract: Many plant tissues contain very low levels of DNA and in such circumstances it is necessary to utilize a method of estimation of extreme sensitivity coupled with a low reagent blank. In this respect it is our experience that the Burton diphenylamine method1 is the most satisfactory. This procedure has been simplified, the blank considerably reduced and the sensitivity increased.
1,978 citations
TL;DR: Structure of Hen Egg-White Lysozyme: A Three-dimensional Fourier Synthesis at 2 A Resolution as mentioned in this paper, 3D Fourier synthesis at 2 a resolution.
Abstract: Structure of Hen Egg-White Lysozyme: A Three-dimensional Fourier Synthesis at 2 A Resolution
1,494 citations
TL;DR: Polycyclic Hydrocarbons Vol. 1, No. 2 as mentioned in this paper, with a chapter on carcinogenesis by Regina Schoental. Pp. lvii + 487.
Abstract: Polycyclic Hydrocarbons Vol. 1. Pp. xxvi + 487. 126S. (With a chapter on carcinogenesis by Regina Schoental.) Vol. 2. Pp. lvii + 487. 140s. By E. Clar. (London and New York: Academic Press; Berlin: Springer-Verlag, 1964.)
1,175 citations
TL;DR: In this article, the authors proposed the notion of dextral transform faults, which can be seen as a pair of half-shears joined end-to-end, which is the case of the San Andreas Transform Fault.
Abstract: T and half-shears. Many geologists1 have maintained that movements of the Earth's crust are concentrated in mobile belts, which may take the form of mountains, mid-ocean ridges or major faults with large horizontal movements. These features and the seismic activity along them often appear to end abruptly, which is puzzling. The problem has been difficult to investigate because most terminations lie in ocean basins. This article suggests that these features are not isolated, that few come to dead ends, but that they are connected into a continuous network of mobile belts about the Earth which divide the surface into several large rigid plates (Fig. I). Any feature at its apparent termination may be transformed into another feature of one of the other two types. For example, a fault may be transformed into a mid-ocean ridge as illustrated in Fig. 2a. At the point of transformation the horizontal shear motion along the fault ends abruptly by being changed into an expanding tensional motion across the ridge or rift with a change in seismicity. A junction where one feature changes into another is here called a transform. This type and two others illustrated in Figs. 2b and c may also be termed half-shears (a name suggested in conversation by Prof. J. D. Bernal). Twice as many types of half-shears involve mountains as ridges, because mountains are asymmetrical whereas ridgos have bilateral symmetry. This way of abruptly ending large horizontal shear motions is offered as an explanation of what has long been recognized as a puzzling feature of large faults like the San Andreas. Another type of transform whereby a mountain is transformed into a mid-ocean ridge was suggested by S. W. Carey when he proposed that the Pyrenees Mountains were compressed because of the rifting open of the Bay of Biscay (presumably by the formation of a midocean ridge a.long its axis). The types illustrated are all dextra.l, but equivalent sinistral types exist. In this article the term 'ridge' will be used to mean midocean ridge and also rise (where that term has been used meaning mid-ocean ridge, as by Menard\" in the Pacific basin). The terms mountains and mountain system may include island arcs. An arc is described as being convex or concave depending on which face is first reached when proceeding in the direction indicated by an arrow depicting relative motion (Figs. 2 and 3). The word fault may mean a system of several closely related faults. Transform faults. Faults in which the displacement suddenly stops or changes form and direction are not true transcurrent faults. It is proposed that a separate class of horizontal shear faults exists which terminate abruptly at both ends, but which nevertheless may show great displacements. Each may be thought of as a pair of half. shears joined end to end. Any combination of pairs of the three dextral half-shears may be joined giving rise to the six types illustrated in Fig. 3. Another six sinistral forms can also exist. The name transform fault is proposed for the class, and members may be described in terms of the features which they connect (for example, dextral transform fault, ridge--convex arc type). The distinctions between types might appear trivial until the variation in the habits of growth of the different types is considered as is shown in Fig. 4. These distinctions are that ridges expand to produce new crust, thus leaving residual inactive traces in the topography of their former positions. On the other hand oceanic crust moves down under island arcs absorbing old crust so that they leave no traces of past positions. The convex sides of arcs thus advance. For these reasons transform faults of types a, b and d in Fig. 4 grow in total width, type f diminishes and the behaviour of types c and e is indeterminate. It is significant that the direction of motion on trarn,form faults of the type shown in Fig. 3a is the reverse of that required to offset the ridge. This is a fundamental difference between transform and transcurrent faulting.
1,137 citations
TL;DR: microscopic investigations suggest that there are three types of patches of membrane density in the synaptic contacts of the central nervous system, of which only two are functional (Gray's type 1 and type 2), but no criterion has yet been established to distinguish the excitatory synapses from the inhibitory ones.
Abstract: ELECTRON microscopic investigations by Gray1,2, De Lorenzo3 and Hamlyn4 suggest that there are three types of patches of membrane density in the synaptic contacts of the central nervous system, of which only two are functional (Gray's type 1 and type 2). However, no criterion has yet been established to distinguish the excitatory synapses from the inhibitory ones. In the peripheral autonomic nervous system two types of synaptic vesicles (cholinergic and adrenergic) have been found, the former having a diameter of 500 A with clear content, while the latter have a diameter of 1000 A with granular cores5–7. So-called granulated vesicles have also been discovered by Shimizu8 in the hypothalamus of mammals. Gray's classification hints that the type 1 synapse is excitatory, whereas the type 2 is inhibitory9.
887 citations
TL;DR: The results of the present work indicate that in many if not all mammalian species the culture of liberated oocytes for periods longer than 20 h will induce a resumption of meiosis at a rate exactly comparable to that occurring in vitro after an injection of LH into the mother.
Abstract: T HE investigation of early development in many mammalian species is restricted by the difficulty of obtaining sufficient numbers of oocytes and embryos at particular stages of development. Post-dictyate ovarian oocytes are usually obtained after stimulation by luteinizing hormone (LH) either during the female cycle or after the injection of exogenous hormone, and ovulated eggs can be obtained in relatively large numbers after superovulation treatments. While these methods are highly satisfactory for many types of investigation, they are obviously unsuitable in the examination of species such as primates or man where the effect of exogenous hormones is undesirable or inadequately understood and in experiments demanding very large numbers of oocytes. An alternative technique has been reported in rabbits1 and rodents2 , namely, to liberate the oocyte from its follicle into a culture medium whereon the prolonged dictyate stage is abruptly terminated, the germinal vesicle breaks down, and meiosis is resumed at diplotene/diakinesis within 2-3 h. But, with dog, primate and human oocytes, the germinal vesicles persisted after 20 h of culture\". The results of the present work indicate, however, that in many if not all mammalian species the culture of liberated oocytes for periods longer than 20 h will induce a resumption of meiosis at a rate exactly comparable to that occurring in vitro after an injection of LH into the mother. With this technique it should eventually be possible to study pre-ovulatory development, and perhaps fertilization and pre-implantation development in various species including man.
811 citations
TL;DR: This species has also been frequently recovered in low counts from South African cereal and legume crops and has been reported as constituents of the mycoflora characteristic of ‘katsuobushi’ and other fermented fish preparations.
Abstract: Aspergillus ochraceus Wilh. is widely distributed in Nature and often found in soil and on decaying vegetation. It is, however, also known to invade stored wheat with moisture contents more than 16 per cent1. In the far east, Asp. ochraceus and allied species have been reported as constituents of the mycoflora characteristic of ‘katsuobushi’ and other fermented fish preparations2. In the United States, Patent No. 1,313,209 covers the use of Asp. ochraceus for its ability to induce a desirable change in flavour during the fermentation of coffee. This species has also been frequently recovered in low counts from South African cereal and legume crops3.
793 citations
TL;DR: Vibration problems in engineering are illustrated with examples friction force and dynamics and vibrations notes free undamped vibrations.
Abstract: dynamics and vibrations notes forced vibrations. vibration problems in engineering s timoshenko google. download free ebook vibration problems in engineering 2nd. vibration problems in engineering barnes amp noble. free pdf vibration problems in engineering 5th edition. vibration problems engineering abebooks. vibration problems in engineering open library. vibration problems in engineering pdf download. kaist lecture 01 2003 university of colorado boulder. vibration problems in engineering w weaver jr s p. vibration problems in engineering 2nd edition s. vibration problems in engineering donovan h young. vibration problems in engineering alibris. vibration problems in engineering s timoshenko. vibration problems in engineering s timoshenko 1937. vibration problems in engineering 3rd ed pdf download. vibration problems in engineering google books. vibration problems in engineering book 1990 worldcat org. mechanical vibration engineering dynamics mechanical. vibration problems in engineering introductory. vibration problems in engineering alla ricerca del. vibration problems in engineering edition 5 by w weaver. vibration problems in engineering by s timoshenko book. timoshenko vibration problems in engineering. vibration problems in engineering by william weaver jr. vibration problems in engineering book by s timoshenko 7. vibration problems in engineering timoshenko s pdf. vibration problems in engineering by timoshenko. vibration problems in engineering timoshenko s free. vibration problems in engineering by stephen p timoshenko. pdf engineering timoshenko vibration problems in. me 563 mechanical vibrations purdue engineering. mechanical vibration solved examples friction force. staff view vibration problems in engineering. vibration problems in engineering 2008 476 pages s. vibration problems in structures flow engineering. vibration problems in engineering machines turbine. vibration problems in engineering timoshenko s free. vibration problems in engineering willkommen. vibration problems in engineering 5th edition. dynamics and vibrations notes free undamped vibrations. 0471873152 vibration problems in engineering 4th. vibration problems in engineering 1st ed pdf download. error found in timoshenko’s vibration problems in engineering. vibration problems in engineering s timoshenko. download vibration problems in engineering 5th edition pdf
747 citations
TL;DR: Alizarin red S in solution is probably the best method of distinguishing between the common carbonates as mentioned in this paper, and it is now known that any carbonate mineral containing small quantities of ferrous iron will stain with potassium ferricyanide providing the carbonate can be made to react with an acid medium.
Abstract: POTASSIUM ferricyanide and alizarin red S are frequently used as stains for distinguishing between carbonate minerals. Potassium ferricyanide in acid solution produces Turnbull's blue with ferrous iron and it used to be thought that dolomite could be distinguished from calcite on the basis that dolomite alone contained ferrous iron. Recently this has been shown to be incorrect1, and it is now known that any carbonate mineral containing small quantities of ferrous iron will stain with potassium ferricyanide providing the carbonate can be made to react with an acid medium. Recent work2,3 shows that alizarin red S in solution is probably the best method of distinguishing between the common carbonates.
685 citations
TL;DR: Hybrid Cells Derived from Mouse and Man : Artificial Heterokaryons of Mammalian Cells from Different Species is presented, which describes how cells from different species can be hybrids.
Abstract: Hybrid Cells Derived from Mouse and Man : Artificial Heterokaryons of Mammalian Cells from Different Species
TL;DR: An investigation of the response of cells in the dorsolateral tract of the cat to C fibres was carried out, finding that an afferent volley in the unmyelinated fibres led to a positive dorsal root potential as opposed to the well-known negative dorsal potential which is elicited by the large myelination fibres.
Abstract: IN the dorsal part of the dorsal horn there is a lamina of cells which respond to cutaneous stimulation and send their axons into the dorsolateral tract. In previous investigations1 it was apparent that many different types of A fibres converged on these cells. It is, therefore, interesting to see whether C fibres also affect their firing. In a recent investigation2 it was found that an afferent volley in the unmyelinated fibres led to a positive dorsal root potential as opposed to the well-known negative dorsal potential which is elicited by the large myelinated fibres. It was suggested that C fibres led to presynaptic hyperpolarization which would produce facilitation as contrasted with the presynaptic inhibitory effects of the A fibres. An investigation of the ventral root reflex (VRR, ref. 2) showed no late component which could be attributed to C fibres; however, a tetanus in the C's was found to potentiate the VRR elicited by the A fibres in the same peripheral nerve. It was also known that a large stimulus to a peripheral nerve led to late discharges in various midbrain and forebrain structures3. With these factors in mind an investigation of the response of cells in the dorsolateral tract of the cat to C fibres was carried out.
TL;DR: In this paper, the authors show which of four abbreviated series approximations most nearly approaches this ideal, and show that the best balance of accuracy and convenience is achieved by the use of series taken to as few terms as possible.
Abstract: THE equation of the plot of thermogravimetric data is useful in kinetic analysis (1–12), but since it contains an exponential integral, many workers prefer approximate expressions. The best balance of accuracy and convenience is achieved by the use of series taken to as few terms as possible, and it is the purpose of this communication to show which of four such abbreviated series approximations most nearly approaches this ideal.
TL;DR: The results presented here support the idea that sublInits are active in polypeptide initiation; but at first sight they tend to contradict the conclusion that monosomcs are inactive.
Abstract: On the other hand, Hardesty et al. 10 and Lamfrom and Knopf\" have suggested that mono somes do initiate globin chains. Under the conditions used by these authors for the preparation of monosomes, sub-units would have been disaggregated. It is likely, however, that the monosomeR 'were not resolved from tho disaggregatcd sub-units. The mOllosomes used by Goodman and Rich 25 in reaching the same conclusion from tlxperiments with an ascites cell systom were marc thoroughly purified. However, it iH not known whether or not ascites cell native sub-units wonld be aggregated under the conditions of isolation. The results presented here support the idea that sublInits are active in. polypeptide initiation; but at first sight they tend to contradict the conclusion that monosomcs are inactive. Monosomes are clearly shown to be active in polyphenylalanine synthesis, although less so than sub-Ul~its. However, it is by no means certain that the properties of poly-U and the endogenolls informat.ional RNA are the same. Secondly, in the experiments Toported here the ratio of poly-U molecules to ribosomes was of the order of 100 : 1. In the endogenous situation it is likely to be less than 1 : 1. The reactivity of tho ribosome fractions with poly-V may not be a certain index of their behaviour either within the cell or ill tho cell-free system without added polynucleotide_ I thank Mrs. Norma Robertson for her assistance, and MI'. B. B. Cohen for his advice. This work was supportcd by grants from the Medical Research Council. 1 Arnstein, H. R. V., Biochem. J., 81, UP (:t (l61). , Glerer, A., J. Mol. Bioi., 6, 148 (1963). 3 Marks, P. A., Burka, E. R ., and SchleSSinger, D., Proc. U.S. Aat . Acad. S\"i., 48, 2163 (1962). • Warner, ,J. Ro, Knopf, P. }l., a.nd Rich, A. , Proc. U. S . Nal. Acad. Sci. , 49 122 (1963). '1'8'0, P. O. P., and Vinograd, J., BiocMm. Biophys. A cta, 49,113 (1961). • Wettstein, }'. 0 ., Staeheliu, T. , a.nd Noll, H., Nature, 197, 430 (1963). , Hi.llOp, J. 0., Biachim. Biopltvs. Acta (in the press). • Warner, .J. Ro, and Rich, A., J. Mol. Bioi., 10, 202 (1964). • Mat.hias, A. 1'., Williamson, R . , Huxley, R . Eo, auu Page , S., .f. Mul. BioI.. 9, 154 (1964). '\" Hardesty, B., Hutton, J. J. , Arlinghuus, R., and Schwcet, R., 1\"(0('. U.s. Nat. Acad. Sci., 50, 1078 (1963). 11 Spyrides , G. J., an.d Lipmann, F., Proc. U.S. ;.. Vat. Acad. Sci. , 48 . 1977 (1962). .. liarondes, S. H., and Nirenberg, ~L W., Sci\",,,e, 138, 813 (1962). 13 Gilbert, W., J. Mol. Bioi. , 6, 374 (1963) . ,. Hardesty, B., Arllnghaus, R ., Schaeffer, J., and Sehweet, R. S., Cold Sprin;] Harbor Symp. Quant. Bioi., 28, 215 (1963). 11 Ra.,chemeyer, A. E. V., and Rich, A. , Biochim. B-iophys. A cta , 55, 9U (1962). .. Bishop, J. 0., Nature, 202, 86 (1964). n J31shop, J. 0., Nature, 203,40 (1964). \"Allcn, E. H., and Sehweet, R. S., .!. Bioi. Chern., 237 , 760 (1962). \" Monicr, Ro, Stephenson, JI{. L., and Zamecnik, P. C., Rim·him. Bi
TL;DR: Recent autoradiographic evidence from the laboratory is described which shows clearly that a large proportion of the short·axoned neurones present in various brain structures are formed after birth in the rat.
Abstract: M ITOTIC neurones are seldom, if ever, seen after birth in the brains of mammals, from which it is com monly concluded that neurogenesis is a pre-natal pheno menon. This conclusion is not often questioned, even though post-natal neurogenesis in some brain structures has been well established for some time. Thus it was recognized in the nineteenth centuryl-3 that a class of smaIl nerve cells, the granule cells, shows a high rate of proliferative activity in the cerebellar cortex in young animals. Likewise, good quantitative evidence was obtained some time ago' of an increase in the total number of nerve cells in the cerebral cortex of rats up to the 20th day after birth. In this article we shall describe recent autoradiographic evidence from our laboratory which shows clearly that a large proportion of the short·axoned neurones present in various brain structures are formed after birth in the rat. In these investigations we injected rats systemically with tritiated thymidine. Thymidine is a specific pre cw'sor of chromosomal DNA and it is incorporated into cell nuclei only when new DNA is formed by cells preparing for multiplication'. 'When animals are injected with tl'~tiated thymidine, the cells proliferating at the time of injection tend to incorporate the administered radio chemical and they thus become 'tagged'. The radio actively labelled cells are then easily identified with fine resolution autoradiography. Moreover, by killing animals after varying periods of survival following the injection, a time-lapse record may be obtained of the fate of the originally labelled cells, such as the kinetics of their re-multiplication, and their migration and transformation. In a pilot study' we made stereotaxic lesions in the lateral geniculate body in rats and then injected a small dose of tritiated thymidine into the lesion area. The
TL;DR: A new technique for routinely making precise, easily located marks is developed and used in localizing Renshaw cells.
Abstract: FOR some years Renshaw cells in the spinal cord have been extensively investigated. While their physiological and pharmacological properties are relatively well known, knowledge concerning their location in the spinal cord is only approximate and is mostly derived from electrophysiological observations1 and indirect anatomical evidence2. From all this work it has been concluded that Renshaw cells are located in the ventral horn medial to motoneurones. For accurate localization of these and other cells within the central nervous system, however, it is necessary to record the electrical activity with microelectrodes which have satisfactory electrical properties, and then to indicate the location of the electrode tip by making, while causing a minimum of damage to the area, a small and easily identifiable mark. A number of techniques have been used for locating the position of microelectrode tips in nervous tissue3. However, most of these techniques require special histological procedures, may be unreliable, or can only be used at the end of an experiment. While the method of Galifret and Szabo4 needs no special histological procedure and can be used several times in an experiment, it makes rather large marks (several hundred μ) and has not proved completely reliable. We have therefore developed a new technique for routinely making precise, easily located marks and have used this technique in localizing Renshaw cells.
TL;DR: The technique of Schade1 is modified so that a grating target is generated on an oscilloscope by supplying suitable signals to the x, y and z axes, and it could be continuously varied both in contrast and fineness without the mean luminance of the screen changing.
Abstract: THIS communication describes experiments in which the threshold contrast of gratings viewed monocularly and binocularly have been determined (Fig. 1). We have modified the technique of Schade1 so that a grating target is generated on an oscilloscope by supplying suitable signals to the x, y and z axes. It could be continuously varied both in contrast and fineness (spatial frequency) without the mean luminance of the screen changing. The energy distribution across the grating varied sinuosoidally. The grating filled a rectangular area subtending 2° by 1.3°, and was surrounded by a circular field of 12° diameter of the same luminance as the oscilloscope screen (80 cd/m2). The screen was viewed from 57 in., and in all the experiments particular care was taken to correct the eye to within 0.12 diopter with spectacle lenses.
TL;DR: Theory of Approximation of functions of a real variable as mentioned in this paper was proposed by A. F. Timan, translated by J. Cossar and J. Berry.
Abstract: Theory of Approximation of Functions of a Real Variable By A. F. Timan. Translated by J. Berry. English translation edited and editorial preface by J. Cossar. (International Series of Monographs on Pure and Applied Mathematics, Vol. 34.) Pp. xii + 631. (London and New York: Pergamon Press, 1963.) 100s. net.
TL;DR: In this article, the authors described procedures for the assay of these three enzymes which will give a more accurate determination of their respective activities than was possible with the assay systems so far known.
Abstract: IN the mucosa of the small intestine, alkaline phosphatase (orthophosphoric monoester phosphohydrolase; EC 3.1.3.1) is known to be mainly localized in the brush border region1,2 while glucose-6-phosphatase (D-glucose-6-phosphate phosphohydrolase; EC 3.1.3.9) is a predominantly microsomal enzyme3. Thus these two enzymes may be used as markers for the assessment of the purity of subcellular fractions obtained in fractionation studies. However, as pointed out by Ginsburg and Hers3 and Triantaphyllopoulos and Tuba4, the assay of glucose-6-phosphatase is complicated by the fact that glucose-6-phosphate may be hydrolysed by more than one enzyme. Similarly, acid phosphatase (orthophosphoric monoester phosphohydrolase; EC 3.1.3.2) and alkaline phosphatase of the intestinal mucosa have a rather broad pH optimum. These two enzymes are therefore difficult to assay accurately by merely choosing buffers of different pH values. These difficulties can be overcome by the use of specific inhibitors. In the following, procedures are described for the assay of these three phosphatases which will give a more accurate determination of their respective activities than was possible with the assay systems so far known.
TL;DR: The physiological Basis of Salt Tolerance of Plants, as Affected by Various Types of Salinity, is described.
Abstract: Physiological Basis of Salt Tolerance of Plants (As Affected by Various Types of Salinity.) By B. P. Strogonov. Translated from the Russian by Prof. A. Poljakoff-Mayber and Dr. S. M. Mayer. Pp. 279. (Jerusalem: Israel Program for Scientific Translations; London: Oldbourne Press, 1964.) 88s.
TL;DR: The Natural Environment Research Council will take over responsibility for the parts of the grants and awards programme that lie within its field, with the emphasis on continuity.
Abstract: a fortunate circumstance that it has proved possible to accommodate the headquarters of both Councils in the same building. For the time being, the machinery of administration will be much the same as hitherto, with the Natural Environment Research Council taking over responsibility for the parts of the grants and awards programme that lie within its field. The emphasis on continuity should be particularly welcomed by universities and others concerned with this important aspect of the Government's policy for science.
TL;DR: The theory that carbonate groups substitute for the phosphate groups in the apatite structure of both the mineral carbonate apatites and the calcified tissues of teeth and bone is compatible with the decreased a-axis which accompanies CO3 inclusion in the mineral apatITE.
Abstract: THE mode of carbonate substitution into the apatite structure of calcified tissues has been a controversial issue for many years. McConnell has advanced the theory that carbonate groups substitute for the phosphate groups in the apatite structure of both the mineral carbonate apatites (for example, dahllite, staffelite or francolite) and the calcified tissues of teeth and bone1,2. This theory is compatible with the decreased a-axis which accompanies CO3 inclusion in the mineral apatites3. (An a-axis contraction can be expected when the smaller planar CO3 group substitutes for the larger tetrahedral PO4 group.)
TL;DR: The purpose of this communication is to report the findings in a survey of mentally sub-normal male patients with dangerous, violent or criminal propensities in an institution where they are treated under conditions of special security.
Abstract: IT is well known that 1 per cent of males in institutions for the mentally sub-normal are chromatin-positive and that the majority of these have an XXY sex chromosome constitution1. In 1963 Forssman and Hambert2 reported on a survey of the nuclear sex of 760 male patients in three Swedish institutions for criminal and ‘hard-to-manage’ males of sub-normal intelligence. They found 2 per cent to be chromatin positive, but the chromosome constitution of these patients was not reported. Casey (personal communication) surveyed 942 males in two comparable institutions in England, and found 2.2 per cent of them to be chromatin-positive. He also studied the chromosomes of these 21 chromatin-positive males and found 7 to have either an XXYY sex chromosome constitution or to be mosaics in which the XXYY cells formed the major cell line. This finding of a third of the chromatin-positive males to have an XXYY cell line contrasted sharply with that of Maclean and his colleagues1, who studied 2,607 ordinary mentally sub-normal males, and found only 2 of the 28 chromatin-positive patients to have an XXYY constitution. This contrast led us to wonder whether an extra Y chromosome predisposes its carriers to unusually aggressive behaviour. We decided that if this were the case, then we might expect an increased frequency of XYY males among those of a violent nature. The purpose of this communication is to report our findings in a survey of mentally sub-normal male patients with dangerous, violent or criminal propensities in an institution where they are treated under conditions of special security.