CHEMICAL CHANGES PRODUCED BY MICROORGANISMS. 23 



From facts already considered it will be evident that micro- 

 organisms have properties that certainly fit them for this work. 

 They feed, not upon minerals, as a rule, but upon the organic 

 material in nature; and each kind of organic food, proteid, sugar, 

 starch, wood, etc., is especially subject to the attack of one of the 

 classes of fungi. We have seen'also what inconceivable powers of 

 multiplication are possessed by^bacteria, and, while the other or- 

 ganisms do not grow so fast, they are all rapid growers. While they 

 are growing and multiplying with such vigor, they are producing 

 profound changes in the chemical nature of the food upon which 

 they are feeding. 



CHEMICAL CHANGES PRODUCED BY MICRO- 

 ORGANISMS. 



The chemical changes thus brought about are very numerous. 

 The chemist of to-day has hardly begun to study them, and his 

 knowledge is, as yet, very fragmentary. Only a very few of them 

 are understood, and in regard to the simplest of these our knowledge 

 of the phenomena is yet lacking in many important respects. A few 

 only, bearing directly upon the subject of agriculture, will be ex- 

 plained. They may be grouped under two quite distinct heads. 



Synthetic Processes. Anabolism. These consist in the 

 building of complex bodies out of simpler ones. The fundamental 

 importance of synthetical processes to the continuance of life is 

 evident enough. The animal kingdom, in general, demands complex 

 compounds as foods, and cannot live upon the simple compounds 

 found in the air and the soil, like carbonic dioxide, nitrogen, am- 

 monia, etc. (CO 2 , N, NH 3 ). In order that animals may use the 

 elements existing in nature, some process must build them into 

 complex bodies. This is largely accomplished by the green plants 

 that furnish animals with food. But even these plants demand 

 some of their food in a complex form, not being able, for example, to 

 use nature's free nitrogen store in the atmosphere until it has been 

 built up into some compound like nitric acid. The constructive 

 or synthetic processes are thus of fundamental importance to the life 



