32 BACTERIOLOGY. 



dry stage, may be completely deprived of their water 

 without causing them to lose the power of reproduction 

 when favorable conditions reappear. 



The closer study of the bacteria, and a more intimate 

 acquaintance with their nutritive changes, demonstrate 

 an appreciable variability in the character of the sub- 

 stances best suited for the nutrition of different species, 

 one requiring a tolerably concentrated form of nutri- 

 tion, while another needs but a very limited amount of 

 proteid substance for its- development. Certain mem- 

 bers bring about most profound alterations in the media 

 in which they exist, while others produce but little 

 apparent change. In one case alterations in the reac- 

 tion of the media will be conspicuous, while in an- 

 other no such variation can be detected. With the 

 growth of some forms products resulting from pro- 

 cesses of fermentation appear. Other varieties produce 

 poisons of remarkable degrees of toxicity, while the 

 growth of others may be accompanied by the bodies 

 characteristic of putrefaction. 



For the normal development of bacteria it is not only 

 essential that the sources from which they can obtain the 

 necessary nutritive elements should exist, but account 

 must also be taken of the products of growth of the 

 organism in these substances, Nitrogen and carbon 

 compounds in the proper form to be taken up and 

 appropriated by the organism may exist in sufficient 

 quantities, and still the growth of the organism after a 

 very short time be entirely checked, owing to the pro- 

 duction during their growth of substances inhibitory to 

 their further development. Most conspicuous are the 

 changes produced by the growing bacteria in the chemical 

 reaction of the media. Since the majority of them grow 



