28 GENERAL MORPHOLOGY AND BIOLOGY. 



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 solu- 

 tions, though the process of destruction always goes further, 

 and still simpler substances 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 putre- 

 factive processes, have a similar digestive capacity. When 

 carbohydrates are being split up, then various alcohols, 

 ethers, and acids are produced. During bacterial growth 

 there is not unfrequently the abundant production of such 

 gases as sulphuretted hydrogen, carbon dioxide, methane, 

 etc. 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 pre- 

 cise 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 pro- 

 duction by them of ferments of a very varied nature 

 and complicated action. Thus the digestive action on 

 albumins depends on the production of a peptic ferment 

 analogous to that produced in the animal stomach. Fer- 

 ments which invert sugar, which split sugars up into alcohols 

 or acids, which coagulate casein, which split up urea into 

 ammonium carbonate, have all been isolated from different 

 bacteria. 



Such ferments may be diffused into the surroundmg 

 fluid, or be retained in the cells where they are made. 

 Sometimes the breaking down of the organic matter appears 

 to take place within, or in the immediate proximity of, the 



