27 



EXPEEIMENT II. 



Clean Colchester Oysters. One oyster well brushed on out- 

 side and prepared in the manner already described, -^ part of 

 the oyster contained no microbes capable of growing at 37 C. 

 on Drigalski medium, that is, it contained no B. coli or any 

 microbes forming blue colonies on that medium. The rest 

 (25) had been also thoroughly brushed on the outside under 

 the tap and then placed in clean tub in sea water (4000 c.c.) 

 to which previously, while sterile, emulsion of a pure culture 

 of B. typhosus had been added to the extent that each cubic 

 centimetre contained 744,000 B. typhosus. This determina- 

 tion was made in the following manner : to the 4000 c.c. of 

 sterile sea water were added 4 c.c. of a turbid emulsion of 

 B. typhosus, prepared by well shaking up the growth covering 

 the surface of 48 hours' old agar culture of B. typhosus with 

 10 c.c. of sterile sea water. Immediately after the addition 

 of the 4 c.c. of the typhoid emulsion to the 4000 c.c. of 

 sterile sea water and well shaking it up, 1 c.c of the infected 

 water was added to 99 c.c. of sterile distilled water, and of 

 this dilution -j^ c.c. was used for one Drigalski plate. After 

 48 hours' incubation the colonies, all of B. typhosus, were 

 carefully counted and found to amount to 744, so that 

 1 c.c. of the infected sea water contained 744 x 10 X 100 = 

 744,000 B. typhosus. 



The oysters having been kept in the infected sea water 

 for 24 hours were taken out, well rinsed on the outside and 

 drained, were divided in two lots, one lot (12) were placed in 

 the cool chest dry, the other lot (12) were transferred to a 

 clean tub sterilised by steam, supplied with 2000 c.c. of 

 sterile sea water, and the remaining oyster 1 was, after well 

 brushing it under the tap, used for analysis. The oyster 

 having been opened with a sterile knife, and the fluid drained 

 off as carefully and as well as possible, the whole fish was 

 finely minced with sterile scissors. Total amount of turbid 

 fluid drained off of the minced material was 1 75 c.c. ; from 

 this made two Drigalski plates each with 150 cubic milli- 

 metres. After incubation the enumeration of the two plates, 



