38 



every 24 hours, there were still B. typhosus recovered, 

 whereas in Experiment III we started with 84,000 per 

 oyster i.e., more than twice the number after reinfection, 

 and could discover no B. typhosus three days after change 

 to clean water. 



The previously dry oysters, on the other hand, do not seem 

 to have acquired this power of dealing rapidly with the in- 

 gested B. typhosus during the first 24 hours (1,318,000 after 

 24 hours in infected water), and it took them an appreciably 

 longer time to clean themselves although kept in clean water ; 

 this can be easily understood if we remember that these 

 oysters had, before reinfection, been kept out of the water 

 for nine days, that is, under abnormal conditions. This may 

 well have detracted from the power of their tissues to regain 

 their full activity when replaced in clean water. 



All the oysters of this Experiment III, like those of Ex- 

 periment II, on opening, looked quite normal, plump and 

 juicy, and their shells well and tightly closed. 



EXPEEIMENT IV. 



By this experiment it was sought to ascertain whether 

 oysters at starting sewage-polluted, that is, coming from 

 distinctly sewage-polluted beds, behaved in the same or 

 different way in regard to B. typhosus. For this purpose 

 oysters were taken from the foreshore of Southend, which, 

 as also other shellfish of the same locality, Dr. Nash, the 

 Medical Officer of Health for Southend, had distinctly 

 declared as sewage-polluted and dangerous, and against the 

 consumption of which he gave emphatic warning by public 

 placard. 



Most of these Southend oysters (natives) were very small 

 some not bigger than the size of a penny and on the 

 outside extremely dirty. They were well scraped and 

 brushed under the tap till from all parts all mud had been 

 removed as carefully as possible. They were then placed in 

 a clean tub and covered with sterile sea water (2000 c.c.), to 



