30 WILLIAM M. HAMLET. 



of the day and night. To do this an analyst had to be stationed 

 at the Botany Sewage Farm for some consecutive days ; and as a 

 result, Mr. Doherty made the discovery that at certain hours, 

 nitrites regularly make their appearance, commencing at the early 

 hours of the morning from daylight until ten o'clock in the 

 forenoon. After that hour, they disappear for the rest of the day; 

 again making their appearance next morning. The process of 

 nitrification is no doubt accelerated by light and oxygen, although 

 the nitrifying organisms do their work to some extent in the dark. 

 Many reversible reactions go on in sewage, since as we know 

 that in the process of oxidation of iron in air, ammonia is formed. 

 Ammonia is converted into nitrous and nitric acids. Nitrous and 

 nitric acids change back again into ammonia, while, in some cases 

 even free nitrogen is formed ; but the sequence of changes that 

 happen when human dejecta, along with considerable volumes of 

 water flow into the sewage fermentation-tanks are, that ammonia 

 free and loosely combined, is the main result ; and then, and then 

 only, does the nitric fermentation take place, in two stages ; first 

 the formation of x nitrous nitrogen by B. nitrificans (nitrites), then 

 a period of rest, and then, the final change into nitric nitrogen 

 (nitrates), but, whether the changes are the immediate results of 

 the bacteria themselves, or the result of enzymes secreted or 

 elaborated by the organism, they are symbiotic changes of a 

 remarkable character ; my opinion is, that as in the other processes 

 of fermentation, the enzymes are the immediate cause of the 

 breaking down of proteid matter. 



Notwithstanding the reproach cast upon Sydney by the 

 revelations of her insanitary condition lately brought to light by 

 the Plague in our midst, it should here be recorded that Mr. J. M. 

 Smail, Engineer to the Metropolitan Board of Water Supply and 

 Sewerage, and Mr. Davis, Chief Engineer for Sewerage Con- 

 struction of the Public Works Department, have in looking 



1 From Winogradsky's researches two organisms are concerned in the 

 process of nitrification, M. nitrificans, (Van Tieghem) and two in the 

 process of de-nitrification, B. De-nitrificans a and /3. 



