A manual of hygiene and sanitation . steam sterilizer, pattern of Koch. As a basis for a number of culture-media we may usebeef-broth or bouillon, which is a fluid especially favor-able to bacterial growth in that it contains an abundanceof albumin in solution. When a solid medium is desired,either gelatin or agar-agar (a gelatin-like substance ob-tained from Japan) may be added to bouillon, givingnutrient gelatin and nutrient agar-agar. Of these, the DIFFERENTIATION OF SPECIES. 45 gelatin has a melting-point below the temperature of thehuman body, while that of agar is above ; consequently we
A manual of hygiene and sanitation . steam sterilizer, pattern of Koch. As a basis for a number of culture-media we may usebeef-broth or bouillon, which is a fluid especially favor-able to bacterial growth in that it contains an abundanceof albumin in solution. When a solid medium is desired,either gelatin or agar-agar (a gelatin-like substance ob-tained from Japan) may be added to bouillon, givingnutrient gelatin and nutrient agar-agar. Of these, the DIFFERENTIATION OF SPECIES. 45 gelatin has a melting-point below the temperature of thehuman body, while that of agar is above ; consequently weemploy the latter when it is desired to cultivate germs thatgrow best at the body temperature, although the develop-ment of most bacteria is usually more rapid and charac-teristic upon gelatin. Blood-serum sterilized and solidi-fied is also used for the cultivation of certain organisms, Fig. Arnold steam sterilizer. like the diphtheria bacillus; and there are certain otherswhich can only be identified by their difference in growthupon boiled potato, milk, etc. The differentiation of the various species of bacteria isto be made by noting their appearance and form underthe microscope, whether they are motile or not, how theytake different stains, etc.; by observing their methods ofgrowth in or upon different culture-media, and the colorand appearance of the colonies; by noting whether they 46 BACTERIOLOGY. are aerobic or anaerobic, or facultative, and at what tem-peratures they thrive best, etc.; and finally by studyingtheir action and the effect of their products upon livinganimals. In this way we may determine the characteris-tics of each individual or species, and will eventually havethe data for a strictly scientific classification of the bac-teria in general. For example, the organisms causingsuppuration are usually micrococci, occurring in clusters(staphylococci) or i
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