2 MICROBES AND TOXINS 



and the decompositions and re-combinations of living matter 

 depend entirely upon them. 



Life without microbes is not conceivable at the present 

 day. That does not mean that they were the first living beings 

 to appear on the surface of the earth. It is the more difficult 

 to get an idea of their origin, since in all probability they have 

 undergone evolution, and have not always had the appearance 

 they have at present. It is possible that under forms that we 

 can hardly guess at, life appeared long before the existence of 

 microbial forms ; but microbes have been the chief agents in 

 the spread and extension of life throughout the world. 



In the world of to-day, the building up and breaking down 

 of organic substances are functions of cells, conducted by an 

 infinite number of diastases. These cells include the cells 

 built up into animal and vegetable tissues, and the isolated 

 cells, the microbes. It would not be right to contrast too 

 much the microbial cells with the cells of tissues, merely 

 because the former are separate individuals, whereas the latter 

 are arranged in systems. In nature, micro-organisms can 

 exist as solitary individuals, but are seldom actively at work in 

 this condition. For example, in the soil, the bacteria which 

 fix nitrogen act rather like a wide-spread tissue. The active 

 agents are in any case invariably cells. 



To describe in a few words the cycle which organic matter 

 follows, one cannot do better than quote the celebrated page 

 of Lavoisier, " Plants draw from the circumambient air, from 

 water and in general from the mineral kingdom, the substances 

 necessary for their own organisation. Animals feed either on 

 plants or on other animals, which have themselves fed on 

 plants, so that eventually the matter building them up is 

 always derived either from the air or from the mineral 

 kingdom. 



"Finally, fermentation, putrefaction and combustion are 

 continually restoring to the atmosphere and to the mineral 

 kingdom the elements which plants and animals have 

 borrowed. 



"By what recesses does nature effect this wonderful 



