20 



" hypothetical deduction " apph'ed during the enquiry showed 

 that the epidemic was an " explosive one " (that is, a great 

 number of cases occurred at the same time and not one after 

 the other) ; therefore it was not due to personal infection 

 (that is, the communication, by direct contact, from person 

 to person). Further enquiry gave no reasons for supposing 

 that contaminated water or milk were causes (in which circum- 

 stances the outbreak would have been " explosive "). Two 

 articles of food, however, were consumed by a " considerable 

 proportion " of the patients during the month preceding the 

 onset of illness — these were mussels and fried fish — but further 

 enquiry showed that the mussels might be disregarded. There 

 remained, then, the possibility that fried fish were the means 

 by which the disease had been communicated. 



The fish implicated were plaice which had been caught 

 on the " nursery grounds " of the North Sea, and, as a rule, 

 they were poor quality fish. Plaice are very usually gutted, 

 but it was suggested that, in this case, the process of gutting 

 had been imperfect. These North Sea grounds are, it might 

 be thought, very far away from sources of sewage pollution, 

 yet it was concluded that the possibility of contamination 

 " was not so remote as might at first be supposed." Further, 

 the fish were fried, and this process may be imagined effectively 

 to sterilise small plaice ; nevertheless the contaminating germs 

 assumed to be present in the tissues of the fish were also 

 assumed to have survived the ordeal of boiling oil. 



Such enquiries as this, and the other ones quoted above, 

 are usually very well done. There is a regular technique, and 

 the investigators employed are well-trained men who are 

 thoroughly conscious of the great responsibility of their work 

 and who therefore do that work consistently well. Yet here 

 we have, on the one hand, enteric fever occurring in a mussel- 

 eating population and a causal association established between 

 the mussels and the disease, and, on the other, a group of cases 



