190 Air and Water Poisoning 



The characteristic products of the decomposition of human 

 excreta now demand notice, and attention might have been 

 limited to these if I had not detected the mechanical defects 

 which allowed so much faecal matter to be carried into the 

 streets before decomposition set in, and thus to escape 

 detection, in samples taken immediately from the outflow. 

 The products on which I chiefly relied were carbonic acid, 

 ammonia, and sulphide of hydrogen, which occur free and 

 combined. Carbonic acid and sulphide of hydrogen are 

 yielded by fseces, ammonia and carbonic acid by the decom- 

 position of urine, and all these by albuminous substances. 

 The association of these bodies, especially when, as was the 

 case, nitric acid and sulphurous acid are also found, are 

 satisfactory evidence of the decomposition of excreta, and 

 they were found in every instance. I have not thought it 

 necessary to offer a quantitative determination of either, 

 some would not admit of it, and in no case would a deter- 

 mination have afforded any useful information. I found 

 that there was no constancy in any of the conditions ; that 

 they were found in greater or less amount in every sample 

 examined, and I have therefore no hesitation in pronouncing 

 that the water discharged into the thoroughfares of the city 

 from the closet filters contains more or less of excretal 

 matter in a state of decomposition, and still more which 

 awaits that inevitable natural process. The quantitative 

 results given do not represent all these matters, the free 

 ammonia and other gaseous and volatile matters are given 

 off in the process of estimation. 



My conclusions weie further assisted by the microscopic 

 analyses, which, though laborious, were to my mind of too 

 great importance to be neglected. They are, in fact, as 

 essential as the chemical examinations, for the substances 

 found show whence the water came, and the varieties of 

 plants and animals indicate its condition. Now those few 

 organisms which inhabit the Yan Yean water are all healthy, 

 and indicate a sweet pure water, as well by their pre- 

 sence as by the absence of others which are uniformly 

 associated with the decomposition of organic matters of 

 various kinds. In the fresh filtered sewage, on the other 

 hand, the higher organisms of each class appeared in propor- 

 tion to the amount of dilution, and as decomposition set in 

 they gradually died out and were replaced by the lower 

 grades. Thus several of the desmidige and the highly 

 organised rotatoria are found in the fresh sewao;e from the 



