A manual of hygiene and sanitation . anging between 20° and40° C. (68° and 104° F.), though they may grow at anytemperature between 5° and 43° C. (41° and ° F.).Any marked deviation in the culture-media from theneutral point or continued exposure to extremes of tem-perature may either check the growth of the organismsaltogether, and eventually destroy them, or may causespore-formation, or the production of involution-forms,or a change in the composition and the character of thechemical products which the bacteria normally produce. SEPARATION OF SPECIES. 41 This also holds good with respec
A manual of hygiene and sanitation . anging between 20° and40° C. (68° and 104° F.), though they may grow at anytemperature between 5° and 43° C. (41° and ° F.).Any marked deviation in the culture-media from theneutral point or continued exposure to extremes of tem-perature may either check the growth of the organismsaltogether, and eventually destroy them, or may causespore-formation, or the production of involution-forms,or a change in the composition and the character of thechemical products which the bacteria normally produce. SEPARATION OF SPECIES. 41 This also holds good with respect to any other conditionor substance that may be deleterious to the bacteria intheir normal state; wherefore we shall see that it is im-portant as having a decided influence in altering the viru-lence of pathogenic bacteria and in suggesting methods forbringing about a condition of immunity to their attacks. As it is rare to find isolated individual species anywhereexcept in pure cultures artificially prepared, it is evident. spirillum of Asiatic cholera. X 1000. that we must devise some way of separating the differentkinds of organisms one from another. This is bestaccomplished by the method suggested by Koch, viz., tointroduce the mixed kinds into some melted culture-medium, like nutrient gelatin, which solidifies on cooling,but whose melting-point is not sufficiently high to destroythe vitality of the germs. If the fluid be well shaken,the various species will be distributed through it, and uponcooling each individual or group (zooglea) of individuals 42 BACTERIOLOGY, of the same kind will be fixed in its place and become thestarting-point of a colony of that special kind. Moreover,if the gelatin before cooling be poured upon sterilized Fig. 4.
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