Physiology. 11 



matter, unable to rot and decay would soon bury all un- 

 der the constantly accumulating mass. Owing to the 

 energies of the lower types of plant and animal life, all 

 of this dead effete matter is slowly consumed. The split- 

 ting of these materials into the simpler elements is largely 

 due to the activities of the bacteria. Almost without ex- 

 ception, they prey upon organized matter, absorbing suf- 

 ficient energy for their maintenance, and at the same time, 

 giving off the unused elements to form new combinations 

 that are again absorbed in different forms. 



19. Specialization of bacteria. With the higher plant 

 and animal forms, a certain specialization is in progress. 

 The plant or the animal adapts itself to its environment, 

 and in doing so, each group as a whole acquires certain 

 characteristics that mark it in a greater or lesser degree. 

 Usually, specialization accompanies a complexity of struc- 

 ture, so that the higher developed plants and animals show 

 this characteristic more fully than those that belong to 

 the more primitive types. 



In the bacteria is seen a curious anomaly to this rule. 

 Simple in structure as they appear to be, they surpass in 

 functional variability many of the higher forms of plant 

 and animal life. Ubiquitous in their distribution through- 

 out the realm of nature, they have gradually adapted 

 themselves to the different habitats in which they have 

 found themselves, and as a result, more or less well marked 

 groups are to be found. Thus, there is a normal bacte- 

 rial flora of the mouth, another of the skin, and still 

 another of the intestines. Again, there is a class known 

 collectively as water bacteria, still another that might 

 with propriety be classified as milk bacteria. Those forms 

 that have become habituated to certain conditions, may 

 be said to be indigenous or native to that habitat, while 

 the presence of uncommon forms from some other source 



