Hormonal Control of Lactation
The problems involved in the hormonal control of lactation are extremely complex, and researches now in progress, while adding to our knowledge of the factors at work, have not led to the postulation of any all-embracing or coherent theory. Ample evidence for this statement is given in the comprehensive review by Folley,' to whose work we referred in a leading article on lactation in July of last year. At the moment the chief interest in this country is focused on the actions of oestrogens and pituitary fractions and their relations. It is by now well established that mammary development may be incited in most mammals by combined treatment with an oestrogen and progesterone. In general, oestrogens appear to stimulate duct development and progesterone appears to be responsible for alveolar growth. There is no clear-cut evidence that these actions are direct, for experiments in hypophysectomized animals. have given conflicting results in the hands of different workers. In this connexion Speert2 performed an interesting experiment by painting the left nipples of immature male monkeys with an alcoholic solution of oestrone, the right nipples being painted with alcohol alone. He found that the oestronetreated mammae enlarged while the control right nipples were uiaffected, which goes to show that the pituitary was not involved. This conclusion, however, at present applies only to the mammary glands of the immature male monkey, because one of the most confusing factors in research on lactation has been the quite different results obtained by similar procedures in different species and in the different sexes of the same species. The technique of unilateral inunction does, however, provide a method for testing the direct action of hormones absorbed through the skin without removing the animal's own glands, which inevitably results in undesirable and usually uncontrollable secondary effects. Turning to the question of the secretion of milk by the mammary glands when they are fully developed, the pituitary is found to be accepted as the most important factor at work. It is perhaps unfortunate that the early researches of Riddle showed that anterior pituitary extracts which initiate lactation in a variety of species would also cause the growth of crop-glands in the pigeon. This was made the basis of an assay method for preparations and was almost universally adopted. It is only lately that it has been appreciated that this method of assay has distinct disadvantages. It is now realized that an extract capable of stimulating the pigeon's crop-gland does not necessarily initiate milk secretion in mammals. The commercial preparations of prolactin at present available are usually standardized by the crop-gland response, a fact which may accouint for conflicting clinical reports. Folley' therefore proposes that the name " prolactin " should be confined to crop-stimulating activity, and Folley and Young3 suggest the term " galactopoietic factor " for the anterior pituitary fraction responsible for increasing the milk yield of an animal already producing milk. " Lactogenic " is applied to the initiation of lactation in hypophysectomized animals. Folley and Young in their experiments showed that injections of crude anterior pituitary extracts increase the milk yield in cows in declining lactation to a greater extent than do purer preparations containing seven times as much prolactin (crop-stimulating) activity. This leaves open the question whether prolactin is galactopoietic, but proves that there is a distinct galactopoietic factor in the pituitary apart from a prolactin, or a principle which, acting with prolactin, has a synergistic galactopoietic effect. The present difficulty
AN EXPERIMENTAL STUDY OF THE CAUSES WHICH PRODUCE THE GROWTH OF THE MAMMARY GLAND
Hyperplasia of the breasts is regularly noted in pregnancy. This change in the breasts, for a time passively accepted as a fact, has in late years been made the subject of intensive study, which aimed to discover the primary cause of the tissue growth, and to analyze the nature of the stimulus which gave rise to it. The subject is not only of great interest to biologists, but to investigators in all branches of medicine. The sweeping analogies, drawn from some of the theories which have been based on experimental work, are so far-reaching that confirmation is imperatively needed; otherwise there is danger of basing future research, some in allied, others in entirely separate fields, on an insecure or even false foundation. The breast hyperplasia of pregnancy can best be studied in animals, and as a matter of laboratory convenience, small animals are preferred. Most workers have employed
Optimal Combination and Concentration of Antibiotics in Media for Isolation of Pathogenic Fungi and Nocardia asteroides
Strains of Blastomyces dermatitidis, Sporothrix schenckii, Histoplasma capsulatum, Cryptococcus neoformans, Nocardia asteroides, and Coccidioides immitis were tested for in vitro susceptibility to polymyxin, gentamicin, kanamycin, chloramphenicol, and neomycin at concentrations of 1, 2, 4, 8, and 16 μg/ml. Polymyxin was the most inhibitory and gentamicin was the least inhibitory of the five antibiotics. Two Histoplasma mycelial strains were partially inhibited by 2 and 8 μg of gentamicin per ml and showed at least a 2+ growth at the higher antibiotic concentration. Kanamycin and neomycin produced significant inhibition of N. asteroides but otherwise were noninhibitory. A combination of chloramphenicol and kanamycin, each at 16 μg/ml, and gentamicin, at 4 μg/ml, was noninhibitory to the strains tested except for N. asteroides. Chloramphenicol at 16 μg/ml was not inhibitory for N. asteroides. The results suggest that the optimal antibiotic combination to use in the isolation of fungi and higher bacteria is chloramphenicol, 16 μg/ml, and gentamicin, 4 μg/ml. Addition of sheep blood (5%) had no effect on antibiotic susceptibility of the organisms studied.