28 GENERAL MORPHOLOGY AND BIOLOGY. 



These are known as parasitic bacteria. Sometimes an 

 attempt is made to draw a hard and fast line between the 

 saprophytes and the parasites, and obligatory saprophytes 

 or parasites are spoken of. This is an erroneous distinc- 

 tion. Some bacteria which are normally saprophytes can 

 produce pathogenic effects (e.g., bacillus oedematis maligni), 

 and it is consistent with our knowledge that the best- 

 known parasites may have been derived from sapro- 

 phytes. On the other hand, the fact that most bacteria 

 associated with disease processes, and proved 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 being split up by bacteria undergo 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., indol, 

 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 are pro- 

 duced. During bacterial growth there is not unfrequently 

 the abundant production of such gases as sulphuretted 



