THE METHODS OF BACTERIAL ACTION 23 



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. Many substances 

 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 

 animal stomach. Ferments which invert sugar, which split up 

 sugars into alcohols or acids, which coagulate casein, which split 

 up urea into ammonium carbonate, also occur. 



Such ferments may be diffused into the surrounding fluid, or 



