44 Part III. — Twenty-eighth Annual R6i?0Tt 



Still, I am not aware that either marine, inshore, estuarine, or inland fresh 

 water fish suffer in any appreciable way from the ingestion of sewage bacteria. 

 But it has to be admitted that, although we now have Hofer's "Fischkrank- 

 heiten" as the only published treatise dealing with the diseases of fresh- water 

 fish ; as regards the diseases of marine fish very little has been done and 

 still less written. Certainly, in my own experimental work on both 

 marine and fresh- water fish, I have never found any lesion which I could 

 attribute to the ingestion of bacteria into the alimentary canal, although, 

 this does not exclude the possibilities of the effects of bacterial toxins ; nor 

 in any case in which the peritoneal fluid was examined were bacteria of the 

 intestinal type discovered when the fish were living and in a healthy 

 condition. 



In this respect, however, the evidence given by Professor Herdman before 

 the Royal Commission on Sewage Disposal is both interesting and important. 



While his evidence is in general agreement with the above conclusions, 

 he further stated that, although he had never known of a case of a fish 

 being poisoned by a pathogenic micro-organism, and was of opinion that 

 even if fish were to ingest sewage bacteria in large quantities they would 

 probably show no intestinal lesions, yet at the same time there was the 

 possibility that the bacteria, through their toxins, might cause a lowering of 

 the vitality of the fish. This statement is, of course, an expression of the 

 general mode of action of all bacteria — they may cause local lesions or act 

 through their toxins or by both combined. Herdman, however, makes some 

 differentiations which are not only important from the bacteriological, but 

 also from the point of view of public health. He distinguishes between 

 Pisces or swimming fish and the Mollusca and Crustaceans or shell fish, and 

 considers that in the case of the latter or shell-fish, even although we have 

 as yet no evidence that they suffer in themselves from the ingestion of 

 pathogenic bacteria, yet, since they are so frequently used as articles of food 

 in the raw condition, and consequently often proved to be the medium of 

 transmission of disease, any sewage pollution as regards such fish should be 

 prevented. 



As regards the Pisces or swimming fish, this danger is not present to the 

 same extent ; and in any case such fish are usually cooked, and when 

 properly cooked any such danger of the transmission of pathogenic bacteria 

 is practically precluded. 



Regarding susceptibility, Herdman is of opinion that marine fish are not 

 so susceptible to microbal attacks as fresh-water fish ; and that amongst the 

 former there are degrees of susceptibility, inasmuch as flat-fish are probably 

 less susceptible or show greater resistance to bacterial attacks than round 

 fish, such as haddocks and whitings. 



Of the first proposition I have no experimental evidence ; but regarding 

 the second, certainly my own observations on the reactions of the flat-fish 

 and round-fish respectively to the bacteria, which were the cause of this out- 

 break of disease, and which forms the subject of this investigation, appear to 

 bear out this statement ; and it may be added that in all cases young fish 

 are more susceptible to bacterial poisoning than adult fish. 



Recently a great deal of valuable scientific work, on the question of 

 standards for tidal waters in relation to offensive putrefaction and injury to 

 fish, has been accomplished by Dr. Letts of Belfast and Dr. Adeney of 

 Dublin ; and as these workers have approached the subject purely from the 

 general and chemical points of view, their conclusions are of great interest 

 and importance, when studied along with the bacteriological aspect of the 

 question. 



One of their conclusions, and with which Herdman agrees, has a direct 

 interest, when read in conjunction with the subject of this paper, namely, 

 that, while the discharge of sewage into any river, estuary, or sea-board is 

 in such quantity that its dilution with fresh or sea water is sufficiently large 



