36 OYSTERS AND DISEASE. 



3. To determine the effect of adding various impurities to the water in which the 

 oysters are grown, and especially the effect of sewage in various quantities. It is known 

 that oysters have been sometimes grown or laid down for fattening purposes in water 

 which is more or less contaminated by sewage, but it is still an open question as to the 

 resulting effect upon the oyster. 



4. To determine whether oysters not infected with a pathogenic organism, but 

 grown under insanitary conditions, have a deleterious effect when used as food by other 

 animals. 



5. To determine the effect upon the oyster of infection with typhoid, both 

 naturally, i.e., by feeding with sewage water containing typhoid infection, and artificially, 

 i.e., by feeding on cultures of the typhoid organism. 



6. To determine the fate of the typhoid bacillus in the oyster — whether it is 

 confined to the alimentary canal, and whether it increases in any special part or gives rise 

 to diseased conditions ; how long it remains in the alimentary canal ; whether it remains 

 and grows in the pallial cavity, on the surface of the mantle and branchial folds ; and 

 whether it produces any altered condition of these parts that can be recognised by the 

 eye on opening the oyster. 



7. To determine whether an oyster can free its alimentary canal and pallial cavity 

 from the typhoid organism when placed in a stream of clean sea-water ; and if so, how 

 long would be required, under average conditions, to render infected oysters practically 

 harmless. 



B. The methods which we employed in attaining these objects were as follows : — 



I. Observations upon oysters laid down in the sea at Port Erin : — 



(«) Sunk in 5 fathoms in the bay, in pure water. 

 (/;) Deposited in shore pools, but in clean water. 



(c) Laid down in three different spots in more or less close proximity 

 to the main drain-pipe opening into the sea below low-water mark. 

 These observations were to ascertain differences of fattening, condition, mortality, 

 and the acquisition of deleterious properties as the result of sewage contamination. 



II. Observations upon oysters subjected to various abnormal conditions in the 

 laboratory.* 



{a) A series of oysters placed in sea-water and allowed to stagnate, in 



order to determine the effect of non-aeration. 

 (/>) Similar series in water kept periodically aerated. 

 (c) A series placed in sea-water to which a measured quantity of fresh 



(tap) water was added daily, to determine the effect of a reduction of 



salinity. 



* The oysters were kept in basins, in cool rooms of constant temperature, shaded from the sun, both at 

 the Port Erin Biological Station, and also in the Pathological and Zoological Laboratories at University College, 

 Liverpool. 



