BACTERIOLOGY OF THE OYSTER. 65 



filtered through the gills and so increase the amount of "wash water" 

 for carrying away the bacteria. Also the ciliary motion in the 

 alimentary canal would be hastened and so the organisms contained 

 therein would be more quickly disposed of. Further, the capacity of 

 the oyster to digest and assimulate bacteria would be at its height at a 

 temperature at which the cells are most active. Hence, the optimum 

 temperature for the growth and development of the oyster we would 

 expect to be the period at which all contaminating organisms would 

 be eliminated most rapidly. As the temperature lowers the activities 

 of the oyster lessen accordingly. Further, while above 20°C. the 

 oyster has its valves open most of the time, as the temperature is 

 lowered the oyster is more and more inclined to keep its valves closed 

 for longer and longer periods. This would prevent the mechanical 

 effect of the filtered water in carrying away the bacteria. This 

 mechanical effect is very important for the writer has shown in 

 another part of this paper that bacteria pass through the gills with 

 the filtered water very rapidly. Further, the activity of the cells 

 concerned in the digestion of bacteria would also be less active and 

 also the antagonism between different species of bacteria would be 

 lessened. So it is seen that at lower temperature the tendency would 

 be for oysters to eliminate bacteria more slowly than at higher 

 temperatures. Various opinions have been expressed regarding the 

 temperature at which oysters ''hibernate" or close their shells and 

 remain closed due to the low temperature of the water. The theory 

 of "hibernation" of the oyster was first proposed by Gorham^ to 

 explain the results obtained in his investigation of the sanitary con- 

 ditions of the oyster beds of Narragansett Bay. The temperature 

 at which this phenomenon is supposed to take place is a little above 

 0°C. So far as the writer is aware no experimental work of an exact 

 nature has been done to substantiate or disprove this theory, but 

 from personal observation the writer is led to suspect that the 

 temperature at which the oyster closes its shell for a relatively 

 long period is considerably higher as will appear from one of the 

 experiments detailed below. 



On the other hand, experiments to be detailed later under the 

 hibernation of oysters seem to show that oysters do open and are 

 active at temperatures only one to two degrees above 0°C. It 

 appears that when the temperature is low oysters will close their shell 



1(1) Rep. of Commissioners of Shell Fisheries of R. I., 1910. (2) Seasonal Variation in the 

 Bacterial Content of Oyster.s, Jour. Am. Pub. Health, Jan., 1912. 



