THE METHODS OF BACTERIAL ACTION 23 



to be the cause of the latter, can be grown in artificial media, 

 shows that for a time at least such parasites can be saprophytic. 

 As to how far such a saprophytic existence of disease-producing 

 bacteria occurs in nature, we are in many instances still ignorant. 



The Methods of Bacterial Action. The processes which 

 bodies undergo in being split up by bacteria depend, first, on 

 the chemical nature of the bodies involved, and, secondly, on the 

 varieties of the bacteria which are acting. The destruction of 

 albuminous bodies which is mostly involved in the wide and 

 varied process of putrefaction can be undertaken by whole 

 groups of different varieties of bacteria. The action of the 

 latter on such substances is analogous to what takes place when 

 albumins are subjected to ordinary gastric and intestinal 

 digestion. In these circumstances, therefore, the production 

 of albumoses, peptones, etc., similar to those of ordinary 

 digestion, can be recognised in putrefying solutions, though 

 the process of destruction always goes further, and still simpler 

 substances, e.g., creatinin, indol, and, it may be, crystalline 

 bodies of an alkaloidal nature, are the ultimate results. The 

 process is an exceedingly complicated one when it takes place in 

 nature, and different bacteria are probably concerned in the 

 different stages. Many other bacteria, e.g., some pathogenic 

 forms, though not concerned in ordinary putrefactive processes, 

 have a similar digestive capacity. When carbohydrates are 

 being split up, then various alcohols, ethers, and acids (e.g., 

 lactic acid) are produced. During bacterial growth there is 

 not infrequently the abundant production of such gases as 

 sulphuretted hydrogen, carbon dioxide, methane, etc. One 

 common result of bacterial action is thus an alteration of the 

 reaction of a medium sometimes towards the acid sometimes 

 toward the alkaline side. Reduction phenomena are also 

 frequently observed. For an exact knowledge of the destructive 

 capacities of any particular bacterium there must be an accurate 

 chemical examination of its effects when it has been grown in 

 artificial media the nature of which is known. The precise 

 substances it is capable of forming can thus be found out. 

 Many substances, however, are produced by bacteria, of the 

 exact nature of which we are still ignorant, for example, the 

 toxic bodies which play such an important part in the action of 

 many pathogenic species. 



Many of the actions of bacteria depend on the production by 

 them of ferments of a very varied nature and complicated action. 

 Thus the digestive action on albumins probably depends on the 

 production of a peptic^ferment analogous to^that produced in the 



