A simple theoretical criterion of chemical carcinogenicity?

Summary The simple theoretical criterion for chemical carcinogenicity based on the average quasi-valence number is discussed and shown to be inappropriate as a reliable indicator of carcinogenicity of any organic compound.I thank very much Dr R. Gordon for reading the English text and also for a stimulating discussion.     

An independent microbial flora of the epithelium and its role in the ecomicrobiology of the rumen

IT has been suggested that the bacterial flora of the rumen should be considered as three distinct, interacting populations-the bacteria of rumen fluid (the population which has been studied most extensively), the bacteria associated with food particles, and the bacteria adhering to the epithelial wall of the organ(1). Until now, studies of the 'epithelial' population have been restricted to examination of postmortem samples of wall tissue and its attached bacterial flora(2-5). A recently developed technique(6) for feeding young sheep for long periods solely by infusion of protein and other essential nutrients into the abomasum, and of volatile fatty acids and bicarbonate buffer into the rumen, has provided us with an opportunity to study in isolation the role of the bacterial population of the wall in the ecomicrobiology of the rumen in the living animal. Our studies show that this population can exist independently of the other two populations, that it is primarily responsible for urea digestion in the rumen and that it initiates breakdown of dead epithelial tissue. Furthermore, our results point to an inverse relationship between ammonia concentration and ureolytic activity in rumen fluid, which may account for the control which ammonia exerts over flux of urea across the rumen wall(7-9).     

Neurotransmitter synthesis inLimulus ventral nerve photoreceptors

Summary Radiochemical precursor compounds for neurotransmitters were incubated withLimulus ventral nerve photoreceptor preparations. Octopamine was preferentially synthesized by a photoreceptor rich fraction of the nerve, acetylcholine was made by a photoreceptor poor fraction, and -aminobutyric acid was made about equally well in both fractions. The possibility that the ventral nerve photoreceptor cells serve a neurosecretory function in the adultLimulus is discussed.From the Neurobiology Course, Marine Biological Laboratory, Woods Hole, Mass. The Neurobiology Course is supported by grants from the Grass, Sloan and Sandoz Foundation and from Merck, Sharp and Dohme Research Institute.     

Standardization of "exchange" techniques to measure estradiol receptors in extracts exposed to biospecific adsorbants]

The measurement of the binding of steroid hormone receptors to biospecific adsorbants requires the development of "exchange" techniques. Two types of techniques based on the principle of differential dissociation were standardized: solid phase exchange with hydroxylapatite and liquid phase exchange with adsorption of the ligand to charcoal dextran. In both cases, binding of oestradiol to its receptor was measured in calf uterine cytosol extracts. Results obtained by both techniques were comparable. The half-times of the oestradiol-receptor complex dissociation determined from exchange kinetics are on the same order as those obtained by direct methods used in previous studies.     

The absence of an inhibitory effect of metyrapone (2-methyl-1,2-di (3-pyridyl) propan-1-one) on hepatic microsomal hydroxylation in scurvy.

Microsomes from livers of scorbutic guinea-pigs showed a reduced rate of acetanilide hydroxylation. The response of "scorbutic" liver microsomes to the inhibitor Metyrapone (2-methyl-1,2 di (3-pyridyl) propan-1-one) was different from that of liver microsomes from non-scorbutic guinea-pigs.     

Nuclear pores in the spermatozoon of the rat

Summary The paper describes a hexagonal array of nuclear pores in a non-redundant region of the nuclear envelope underlying the basal surface of the rat spermatozoon head. It is concluded that intranuclear material protruding through these pores is the cause of the characteristic rows of circular bumps found in surface replicas of this region.