XVIIL] NON-PATHOGENIC ORGANISMS. 237 



hydrates, and salts, having become infected with micrococcus, 

 and various species of bacilli, in the first days or weeks 

 chiefly micrococci are present ; afterwards when the micro- 

 cocci have done multiplying and sink to the bottom of the 

 fluid, this latter gradually becomes filled with a variety of 

 bacilli. Or if micrococcus and bacterium termo be sown at 

 the same time in a suitable fluid, we find that at first only 

 the bacterium termo increases rapidly ; afterwards, when this 

 has ceased multiplying, the micrococcus takes the field. In 

 still other cases, as in putrid blood, exudation fluid, par- 

 ticularly in putrefying solid parenchymatous or other 

 substances, various kinds of micro-organisms grow on 

 simultaneously in different parts of the material. 



The same holds good for the zymogenic organisms. A 

 solution containing sugar is a very fit soil for saccharomyces ; 

 when this has exhausted the material, i.e. when all the sugar 

 has been split up into alcohol and carbonic acid, the latter 

 escaping as gas, then the material is ready for the organisms 

 capable of converting the alcohol into acetic acid. The two 

 kinds of organisms may be, however, growing at the same 

 time, the saccharomyces leading. 



Septic or putrefactive organisms then, like zymogenic and 

 pathogenic organisms, are cateris paribus dependent for 

 their growth on the presence of the suitable nourishing 

 material. And, as we have seen, they differ materially from 

 one another in this respect; while putrefactive organisms 

 find in almost all animal and vegetable fluids the substances 

 necessary for nutrition, the zymogenic and pathogenic 

 organisms are much more limited in these respects. Where 

 there is no alcohol present the organisms producing the 

 acetic acid fermentation cannot grow; where there is no 

 sugar or a similar substance present the saccharomyces 

 cannot grow, and so also a particular pathogenic organism 



