178 MICRO-ORGANISMS AND FERMENTATION. 



and Rapp have shown that, whilst a slight motion has a bene- 

 ficial effect on the fermentative activity of yeast, violent 

 mechanical shaking has the effect of materially reducing this 

 activity, the reduction being the more pronounced the poorer 

 the fermenting medium. 



The action of antiseptics on fungi is intimately connected 

 with the activity of the organism and with the temperature. 

 High temperatures augment the injurious effect of the reagent. 

 The degree of concentration of the substance is also of import- 

 ance, for, as already mentioned, minute quantities exercise 

 a stimulating effect. In somewhat greater concentration 

 the growth is retarded, whilst considerable quantities are 

 fatal. 



In apparent contradiction with the above stands the 

 remarkable fact that more concentrated solutions of anti- 

 septics sometimes have a less effect on bacteria than weak 

 solutions ; thus, a 3-5 per cent, solution of cupric chloride 

 killed the spores of the anthrax bacillus in a shorter time 

 than that required by a solution of four times the strength. 



It is also known that different species exhibit a very varied 

 resistance to the same substance, and to the same quantity of 

 that substance. Substances, moreover, which form suitable 

 foods for some species are poisonous to others. A great 

 diversity of behaviour in regard to a particular poison 

 is shown by one and the same fungus in its various stages of 

 development ; bacteria are more easily killed in the vegetative 

 than in the spore condition. Some fungi can withstand a 

 certain amount of poison without their growth being restricted, 

 but under such conditions, or even in the presence of a smaller 

 quantity of antiseptic, they are unable to form reproductive 

 organs. The fungi possess the interesting power of adapting 

 themselves to poisons when they are treated to gradually 

 increasing quantities. An example has been mentioned in 

 Chap. i. (hydrofluoric acid). 



The chemical constituents of fungi are of a most varied 

 nature. Water is the only one occurring almost always in 

 relatively large quantities, the amount in bacteria representing 

 about 80 per cent. (" Mother of Vinegar " forms an exception, 

 and contains 98 per cent.) The yeast group contains from 



