SUMMARY:Mimobes were grown on microscope slides so that the growth could readily be observed by phase-contrast microscopy.ProtGUs &garis, grown on agar containing peNcillin, undergoes extraordinary morphological changes which vary with the temperature of incubation, the concentration of the penicillin, the concentxation of the agar and the presence of small amounts of fluid between the agar and the cover-slip. The bacilli may divide noxznally once or twice into elements that grow without dividing and which may develop into fantastically shaped thread or swollen forms. In high concentrations of penicillin the fantastic shapes are obtained by enlargement without division. At first the nuclei divide as in nomud organisms. The thread forms have condensed nuclei arranged in alternating pattern along the side of the cells. In the swellings there may be either nuclear material Wing the cells, a condensed central mass or a reticulum. When vacuoles are present these displace the nuclear material.When the misshapen organisms are transferred to a medium free from penicillin and containing penicillinase they divide, forming normal bacilli. Many of the swollen elements burst and disappear.The motility of the greatly enlarged organisms is sluggish, and flagellar movement can clearly be observed by phase contrast. The movement of the flagella of the organisms responds readily to radiant heat, and a careful study of these movements makes it impossible to accept Pijper's contention that bacterial motility is due entirely to undulatory movements of the body and that the flagella are merely mucoid strands cast off as the result of motility."he flagella were demonstrated in the large forms by fixing the culture through the s g a~ for several days, detaching the agar and stainingthe cover-slip, which carries the fixed colony, with a saturated watery solution of night blue. The nuclei were shown by treating films with hot nitric acid, washing and staining first with cresyl blue then Leishman's stain.

In the titration of an antibiotic substance it has been usual to choose for the test organism a microbe which. is very sensitive and which is easy to work with. For streptomycin use has been made of Gram-negative bacilli such as B. coli or Friedlander's bacillus, and one strain of Friedlander's bacillus (Klebsiella 41) has been extensively employed in Arnerica. In this article we propose to deal with some of the difficulties we have encountered in the titration of streptomycin in solution or in the patient's serum. We might say here that, as we had no official standard solution of streptomycin, we used for these tests a standard solution made up by dissolving in 100 ml. the contents of one bottle of Merck's streptomycin, which was labelled as containing 1 g. of streptomycin hydrochloride.Influence of the Nature of the Culture Medium For some time we have been using glucose-phenol-redserum water for the titration of penicillin in patients' serum. When streptomycin was titrated in this medium we found that we obtained a much higher end-point than when it was titrated in ordinary broth. We therefore made observations on the bacteriostatic power of streptomycin on a number of different organisms in four different medianamely, (a) ordinary digest broth; (b) peptone water; (c) glucose-phenol-red-serum water (this is made by boiling for a few minutes serum, 2 parts; distilled water, 6 parts; 10% glucose solution, 2 parts; and saturated solution of phenol red, sufficient to give a red colour); (d) defibrinated human blood, inactivated.In regard to the first three media serial twofold dilutions of the stock streptomycin were made in the media which had been inoculated with 10 c.mm. per ml. of a 24-hour culture of the test organism. This was done in 0.5 ml. quantities in test-tubes. With broth and peptone water the end-point was the appearance of-visible growth after 24 hours. In the serum water there was a colour change from red to yellow, and a precipitation of the medium where the organisms grew and fermented the glucose.When the test was made in blood the streptomycin was diluted in saline in 25-c.mm. volumes; these were mixed with the same volume of blood which had been suitably infected with the test organism, and incubated in slide cells. As the growth of Friedlander's bacillus in blood is not very obvious 2% glucose was added when testing this organism: When growth then occurred the blood was haemolysed and a good end-point obtained. The results are shown in Table I.

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SUMMARY: When young cells of a strain of a staphylococcus were exposed to substances noxious to the organism, variations transmissible to progeny were obtained. The variations consisted mainly in a decrease in antibiotic resistance and mouse virulence. Characters of pathogenic strains such as coagulase production, mannitol fermentation and gelatin liquefaction were also abolished.The experiments were carried out in a way that excluded the selection of spontaneous mutants. Adaptation should also be excluded as all variations consisted in a loss or decrease of activities.The variants when first isolated seemed unhealthy, the largest part of their progeny being non-viable and consisting of cells which grew up to a point and lysed without dividing. The results obtained were therefore attributed to a damage of the parent cell caused by the injurious agents used.Antibiotics and other substances noxious to bacteria can induce changes in bacterial cells which are transmissible to progeny for a variable number of generations. The changes have been attributed to a profound disturbance or injury of the parent cell, and in one instance it had been possible to follow, step by step, the evolution of the disturbed cells (Voureka, 1951).The present paper deals with a strain of staphylococcus in the progeny of which decrease of virulence and of resistance to penicillin and to streptomycin were noticed after young growing cells were exposed to injurious agents.New biological characters appeared in a few or in all the colonies grown from the treated cultures. In some cases, the new characters remained unchanged through over 50 passages in normal laboratory media, while in others the variant cell acquired one or more of the characters of the parent. EXPERIMENTALTo exclude, as far as can be done, the possibility that the effects obtained were due to selection of spontaneous mutants endowed with the new characters, the experiments were planned as illustrated schematically in Fig, 1.Freshly isolated cultures derived from one pair of cocci were used in order to have as uniform a population as possible, and the experiments were carried out on a small number of cells so that all the colonies from both the control and the treated bacterial suspension could be examined.The strain selected was a coagulase-positive, phage typable, mouse virulent strain of StaphyZococcus aureus, fermenting mannitol, liquefying gelatin, producing penicillinase and giving a clear-cut zone of haemolysis on horse blood agar; it was resistant to 400 units of penicillin and to 10 units of strepto-