16 Transactions of the Society. 



of the higher plants and animals there is no doubt that many 

 forms of life take part, but when at length these have lived and 

 disappeared, bacteria continue the processes, and it is, as I have 

 remarked, by their action that the organic matter is caused to 

 assume its final form in which it may remain for any period inno- 

 cuous to all forms of life. The brown matter which remains after 

 decay has run its course, consists mainly of the lifeless remains of 

 bacteria. 



Disintegration by bacteria begins in the living organism itself. 

 There is no part of the alimentary canal or of any of the ducts, 

 tubes, or cavities opening into it, in which multitudes of these 

 organisms, growing and multiplying in countless millions, cannot 

 and at all times be found. It has undoubtedly been assumed by 

 many observers that whenever bacteria are discovered in the 

 cavities, tissues, and organs of living animals they have been 

 introduced from without. But the assumption and the conclusions 

 based upon it are erroneous, as any one who will make the investi- 

 gation with due care may easily convince himself In the cavity 

 of the mouth they are always and in all states of health in all 

 animals growing and multiplying excessively. Even in the 

 interior of the cells of plants, cabbages, lettuces, watercresses, &c., 

 as well as in the interstices of the inmost tissues of the higher 

 animals and of man, they or their germs exist, and when the con- 

 ditions become favourable, they grow and multiply in enormous 

 numbers. Many of the bacteria present in the water and in the 

 mud of the river have no doubt been derived from bacteria which 

 existed in the excrementitious matter before it left the organism 

 in which it was formed. These probably go on growing and 

 multiplying in the organic matter while in the Thames, and are 

 not the least important agents in its disintegration and ultimate 

 resolution into harmless compounds. 



Practical Considerations. 



In conclusion, I shall venture to make a few observations con- 

 cerning the practical inferences which are suggested by the present 

 inquiry. Although no doubt a physician is likely to take a 

 rather limited, fragmentary, and possibly not impartial view of 

 many of the most important matters which bear upon the great 

 question of the proper disposal of sewage, while to effectually 

 grapple with the difficulties, engineering knowledge and skill are 

 required which none but the trained engineer can possess, it neverthe- 

 less seems permissible, and since no harm can thereby result, I think 

 it may be desirable that those engaged in other departments of the 

 inquiry should briefly give expression to their views. The subject 

 is one which cannot receive too much consideration before the mode 



