A manual of hygiene and sanitation . y decolorized by aweak solution of nitric acid, as are almost all other bacteria liquefy nutrient gelatin, others do not, andalmost none liquefy agar-agar. This liquefaction is not amelting, but rather a probable peptonization, since thegelatin will not solidify after this occurs, as it does afterbeing subjected to moderate warming. Again, some bac-teria produce one particular color or chemical substance inthe presence of oxygen, and another in its absence; someproduce color only in the light, others only in the dark,etc. Finally, different pat
A manual of hygiene and sanitation . y decolorized by aweak solution of nitric acid, as are almost all other bacteria liquefy nutrient gelatin, others do not, andalmost none liquefy agar-agar. This liquefaction is not amelting, but rather a probable peptonization, since thegelatin will not solidify after this occurs, as it does afterbeing subjected to moderate warming. Again, some bac-teria produce one particular color or chemical substance inthe presence of oxygen, and another in its absence; someproduce color only in the light, others only in the dark,etc. Finally, different pathogenic microbes cause differ-ent maladies when inoculated in animals or human beings. FUNCTIONS OF SAPROPHYTES. 47 and the same germ may produce diiFerent results in ani-mals of different species or families.^ The subdivision of the bacteria into saprophytes andparasites has already been noted. Therefore, it must beremembered that not all of these microscopic plants aredisease-producers; much the larger proportion, in fact, Fig. Pocket-case containing sterilized culture-tubes, platinum needle, andalcohol lamp, used for obtaining cultures for diagnosis, etc. being benefactors rather than otherwise to the human race. The function of many of the saprophytic organismsis to change dead organic matter into simpler chemical ^ See Kenwoods Hygienic Laboratory, pp. 466-470; also McFarlandsPathogenic Bacteria, pp. 46-57. 48 BACTERIOLOGY. compounds and ultimately into end-products such as carbondioxide, ammonia, and water, these latter substances beingonce more utilized in the nutrition of the higher formsof vegetable life, which are in turn necessary to the exist-ence of the animal life upon the globe. One should alsounderstand that some of the saprophytes in the soil seemto possess a constructive or synthetic power, elaboratingmore complex plant-foods from the simple compounds men-tioned. Indeed, it is only M^hen the student of hygienefairly realizes the wide scope of the functions
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