The President's Address. By G. S. Woodhead. 



217 



experimental solutions at intervals of from half a minute up to 

 twenty minutes, and it has been found that an enormous amount 

 of work is done in the first half minute, that at the end of five 

 minutes, only the most resistant specimens of the B. c. c. remain, 

 and that at the end of ten minutes the whole of them have been 

 killed (see fig. 24). In allowing twenty minutes for the sterilization, 



/too 



I 3 00 



80V . 



4<w .. 



Roughly Filtered Cam Water 

 [reafcd With" 1 in a tyllion Chlorine 



Jb Aug I9'k 

 Bile Salt* Agar cultures, 



I division *■ U-0 colonies 



Chlorine neutralized With Ih'iosulfshafi of Joda 

 ar Iffe end oj each period 





ICV 

 of- 



iS minu/fi 



Fig. 24. — Chart giving fall of total number of organisms per c.c. of water from 

 16,000 to 45. All B. c. c. have been eliminated by the " chlorine treatment." 



then, it is evident that provision is made for a working margin of 

 ten minutes after sterilization has been completed. It is now re- 

 ci ignized that the chloride of lime sterilization process is the result of 

 oxidation, and that not only living bacteria but dead organic matter 

 in solution appropriate the oxygen, some of it very rapidly. Con- 

 sequently, wherever organic matter is present in water it is 

 necessary to use a larger proportion of the hypochlorite of lime in 

 order to effect complete sterilization (see fig. 22). Should there be 



