. Pathogenic micro-organisms, including bacteria and Protozoa; a practical manual for students, physicians and health officers. plates are made from a general mixture of all bacteria, selected,as a rule, from the drier portion of the serum. Still others are inocu-lated from the pellicles of ascitic broth cultures. The plates are leftin the incubator for about sixteen hours at 37° C. In the examinationof the plates one should first seek for typical colonies, then if these arenot found, for any that look most nearly like the characteristic colonies are very apt to be
. Pathogenic micro-organisms, including bacteria and Protozoa; a practical manual for students, physicians and health officers. plates are made from a general mixture of all bacteria, selected,as a rule, from the drier portion of the serum. Still others are inocu-lated from the pellicles of ascitic broth cultures. The plates are leftin the incubator for about sixteen hours at 37° C. In the examinationof the plates one should first seek for typical colonies, then if these arenot found, for any that look most nearly like the characteristic colonies are very apt to be found at the edges of the streaksof bacterial growth. The pickings from the colonies are inoculatedupon Loefflers blood serum, or into ascitic bouillon. Growth in Bouillon.—The diphtheria bacilli from about _ one-half thecultures grow readily in broth slightly alkaline to litmus: the other culturesgrow feebly. The characteristic growth in neutral bouillon is one showingfine grains. deposit along the sides and bottom of the tube, leaAnngthe broth nearlv clear. A few cultures in neutral bouillon and many in alka-. THE BACILLUS OF DIPHTHERIA. 201 line bouillon produce for twenty-four or forty-eight hours a more or less diffusecloudiness, and frequently a film forms over the surface of the broth. Onshaking the tube this film breaks up and slowly sinks to the bottom. Thisfilm is apt to develop during the growth of cultures which have long beencultivated in bouillon, and, indeed, after a time the entire development mayappear on the surface in the form of a friable pellicle. The diphtheria bacil-lus in its growth causes a fermentation of meat-sugars and glucose, and thusif these are present changes the reaction of the bouillon, rendering it distinctlyless alkaline within forty-eight hours, and then, after a variable time, when allthe fermentable sugars have been decomposed, more alkahne again throughthe progressing fermentation of other substances. Among the productsformed
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