64 



and in that one there was only one colony of B. coli com- 

 munis per one-tenth part of the body of the oyster. And it 

 is precisely on account of the ready and reliable manner in 

 which B. coli communis can be identified by the method of 

 Drigalski plates that the greatest importance attaches itself 

 to this method. 



Having ascertained, then, that our small Dutch natives 

 contain no B. coli communis, they were divided in two lots : 

 one (five oysters) was kept in sterile sea water (2000 c.c.) 

 without any addition, the other lot (five oysters) was trans- 

 ferred to a fresh tub with sterile sea water (2000 c.c.) to 

 which 5 c.c. of crude sewage (of St. Bartholomew's Hospital) 

 were added. Analysis of this sewage made by Drigalski 

 plate at the same time showed that it contained 220,000 

 B. coli communis per 1 c.c. that is to say, each cubic centi- 

 metre of the infected sea water contained 550 B. coli com- 

 munis. The first lot of oysters, viz., in clean tub with clean 

 sea water, will be mentioned here as " clean lot," the second 

 lot, mz. t in sewage polluted sea water, will be mentioned as 

 "polluted lot." 



Oyster 1 (clean lot) kept 1 day in sea water, contained no 

 B. coli communis. 



2 (polluted lot) kept 1 day in sewage polluted water, 

 contained 800 B. coli communis. 



3 (clean lot) kept 2 days in clean sea water, contained 

 no B. coli communis. 



4 (polluted lot) kept 2 days in polluted sea water, con- 

 tained 150 B. coli communis. 



The polluted lot were taken out after having been kept 

 48 hours in the polluted water, well rinsed under the tap 

 and transferred to clean tub and 2000 c.c. clean (sterile) 

 sea water. The clean lot received 2000 c.c. fresh sterile sea 

 water, and this procedure was repeated on each of the fol- 

 lowing two days. 



Oyster 5 (clean lot) kept 3 days in clean sea water, contained 

 no B. coli communis. 



