Report on the Bacteriology of Water. 185 



Thames Water after Filtration through Porcelain. 



Un- f 2 flasks in incubator, 

 infected \ „ refrigerator. 



Infected / 5 flasks ^'incubator. 



refrigerator , 



Thames Water after Sterilisation by Steam. 



Un- f 2 flasks in incubator, 

 infected \ „ refrigerator. 



Infected/ 5 flasks in incilbator - 



refrigerator. 



Thus, there were in all 16 uninfected and 37 infected flasks em- 

 ployed. 



Note. — Throughout the subsequent account of the series, all flasks 

 placed in the incubator are designated thus: "II," "21," "31," 

 &c, whilst flasks placed in the refrigerator are distinguished as 

 "1R," "2R," "3R," Ac. 



Examination of the Waters for the Presence of Anthrax. — The bac- 

 teriological examination for the presence of anthrax was in general 

 made by the ordinary process of gelatine plate cultivation. This 

 method of identifying the presence of anthrax is attended with but 

 little difficulty if no other organisms are simultaneously present, as 

 in the case of the waters sterilised by steam, and by filtration through 

 porcelain. The anthrax colonies develop with such facility in the 

 gelatine medium, and are of such a characteristic appearance even 

 to the naked eye, but especially when seen through a low power of 

 the microscope, that no doubt can be entertained as to their identity. 

 On the other hand, the very greatest difficulty attends, as will be seen, 

 the recognition of anthrax in the presence of the ordinary water 

 bacteria, partly because the colonies of some of the latter grow much 

 more quickly than those of anthrax, but especially because many of 

 these water bacteria cause such rapid liquefaction of the gelatine that 

 the greater part, or even the whole, of the film may be destroyed 

 before the anthrax colonies have had time to become visible. In 

 order to overcome this difficulty, I have devised a method of 

 destroying nearly the whole of these liquefying bacteria without 

 injuring more than a part of the anthrax spores, and thus rendering 

 possible the development and recognition of the colonies from the latter, 

 even when they are present in water along with vast multitudes of 

 the ordinary water bacteria. The nature of this special method will 

 be described later. The gelatine plates were invariably incubated at 

 a temperature of 18 — 20° C, and in order to give every opportunity 

 for the anthrax colonies to make their appearance, the incubation was 

 carried on as long as possible. On this account the numerical esti- 

 mation of the other colonies was made a subsidiary matter, and in 

 consequence of the extensive liquefaction which had often taken 

 place, the accuracy of the numbers found has often been interfered 

 with ; in fact, discrepancies in the number of colonies found on dupli- 



