288 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



partially digested fatty matter is often present in faeces. 

 Free fat is readily broken up by bacterial or enzyme action, 

 yielding fatty acids and glycerine, as has been shown in 

 Chapter XI. The higher fatty acids thus produced may 

 be further broken down into soluble fatty acids of lower 

 molecular weight. Soaps also are capable of change, but only 

 very slowly. 



In the case of small installations, attached to institutions 

 such as sanatoria, asylums, etc., where a separate laundry 

 exists, the author's experience strongly favours the separate 

 retention of the soap, by treatment with lime salts, and col- 

 lection of the precipitated lime soaps in specially devised 

 intercepting traps. In such cases also it is desirable to retain 

 the grease waste from the kitchen, which is quite capable of 

 being readily and economically worked up into soap on the 

 spot. The retention of fats, apart from its economic aspect, 

 greatly simplifies the operations on the sewage works, where 

 insoluble soaps are liable to be formed, causing accumulations 

 in the tanks and clogging of the filters which receive the 

 tank effluent. The decomposition of fat also gives rise to an 

 extremely objectionable rancid odour, due to the formation of 

 butyric acid. 



To summarise, therefore, the changes which take place 

 in the anaerobic tank, these are mainly the decomposition and 

 gasification of cellulose, the ammoniacal fermentation of urea, 

 the breaking down to a greater or less extent of more complex 

 nitrogenous substances, and the splitting of fats. These 

 changes are almost wholly due to bacteria and to enzymes, 

 the latter in all probability present in faeces. The changes 

 can be followed by analysis of the sewage and of the deposited 

 sludge. In the liquid sewage it will be found that the free 

 ammonia increases at the expense of the albuminoid ; the 

 oxygen absorbed from permanganate, while possibly not 

 greatly differing at the beginning and end of the process in 

 its total amount, will be found to be distributed in different 



