On the Formation of Multiple Images in the Normal Eye. 241 



12. Although we did not find the Bacillus typliosus in any oysters 

 obtained from the sea or from the markets, yet in our experimental 

 oysters inoculated with typhoid we were able to recover the organism 

 from the body of the oyster up to the tenth day. We show that the 

 typhoid bacillus does not increase in the body or in the tissues of the 

 oyster, and our figures indicate that the bacilli perish in the intestine. 



13. Our experiments showed that sea-water was inimical to the 

 growth of the typhoid bacilli. Although their presence was demon- 

 strated in one case on the twenty-first day after addition to the water, 

 still there appeared to be no initial or subsequent multiplication of the 

 bacilli. 



14. In our experiments in washing infected oysters in a stream of 

 clean sea-water the results were definite and uniform; there was a 

 great diminution or total disappearance of the typhoid bacilli in from 

 one to seven days. 



15. The colon group of bacilli is frequently found in shell-fish as sold 

 in towns, and especially in the oyster ; but we have no evidence that it 

 occurs in mollusca living in pure sea water. The natural inference 

 that the presence of the colon bacillus invariably indicates sewage con- 

 tamination must, however, not be considered established without 

 further investigation. 



16. The colon group may be separated into two divisions : (1) those 

 giving the typical reactions of the colon bacillus, and (2) those giving 

 corresponding negative reactions, and so approaching the typhoid 

 type ; but in no case was an organism giving all the reactions of the 

 B. typhosus isolated. It ought to be remembered, however, that our 

 samples of oysters, although of various kinds and from different 

 sources, were in no case, so far as we are aware, derived from a bed 

 known to be contaminated or suspected of typhoid. 



17. We have shown also the frequent occurrence, in various shell- 

 fish from the shops, of anaerobic spore-bearing bacilli giving the cha- 

 racteristics of the B. enteritidis sporogenes recently described by Klein. 



18. As the result of our work, we make certain recommendations as 

 to the sanitary regulation and registration of the oyster beds, and as 

 to quarantine for oysters imported from abroad. 



" On the Formation of Multiple Images in the Normal Eye." By 

 SHELFOED BIDWELL, M.A., LL.B., F.K.S. Keceived December 

 8, 1898 Eead January 19, 1899. 



[PLATE 5.] 



It is well known that a small bright object for which the eye is not 

 accommodated often presents a multiform appearance, the number of 

 separate images perceived varying in different cases from about six to 



