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Part III. — Twenty -sixth Annual Report 



have some intimate relation with the fact that the susceptibility of fish 

 muscle to the attack of putrefactive micro-organisms and to the consequent 

 decomposition is greater than that shown by mammalian muscle. 



Bacteria in Fish. — The question of the presence or absence of bacteria 

 in the blood and tissues of living healthy animals in a normal condition 

 is a subject which has received a good deal of consideration, and 

 regarding which there is some diversity of opinion. Regarding fishes 

 it has been frequently stated that micro-organisms can exist in their 

 blood and tissues, just in the same way as many well-known parasites 

 which make the blood and tissues of fish their habitat. 



Concerning the parasites of fish there is no ground for contention. 

 They are numerous, and, so far as discovered, their life-histories and 

 habitats are generally well known. During the past ten years the 

 working out of the sporozoan parasites — especially the causal relationship 

 of the myxosporidia to disease in fishes and that of the hsemosporidia to 

 disease in man — constitutes a brilliant chapter in zoological science. 



Regarding bacteria, during the past year I have frequently made 

 microscopic examinations of the blood of different varieties of fish, and 

 although I have occasionally observed rod-like and coccus-like bodies, 

 which were suggestive of bacteria, I have to state that as yet I have not 

 been able to isolate in culture any micro-organisms. 



I have also frequently examined, both microscopically and by cultures, 

 the fresh peritoneal fluid of fishes, when removed immediately after death 

 with aseptic precautions. When due care was taken it was very seldom 

 that I found any micro-organisms present, and in such cases one often 

 finds that the fish are not in good condition, or have the appearance of 

 suffering from some disease or injury. Neither in the fresh, healthy, living 

 muscular tissue have I ever found any micro-organisms, when examined 

 in the same way with due precautions. Consequently, I am persuaded 

 that, excluding the gut, micro-organisms do not exist to any appreciable 

 extent in the tissues or body fluids of fish under normal conditions, 

 although it may be possible that, under any abnormal conditions, the 

 tissues may be unable to destroy some of the bacteria which reach them 

 during life ; or, since the tissues of these animals have great powers of 

 adaptation, they may become tolerant to some. After death, on the other 

 hand, the tissues of fish offer comparatively little resistance to the 

 invasion of putrefactive organisms. For these are soon found multiply- 

 ing in great numbers in the gut and in all the body fluids, and gradually 

 penetrate in amongst the surrounding tissues. 



Products of Bacterial Activity. — Among the products of bacterial 

 activity are some substances of an alkaloidal nature which are very 

 poisonous and have recently been isolated from decomposing fish. It is 

 found that one class of these alkaloids, to which the name mytilotoxin 

 has been given, acts chiefly on the nervous system, paralysing motor 

 nerves like curara, while another class of these acts chiefly on the 

 digestive organs, causing acute gastritis and enteritis. Hence when 

 one has regard not only to the increasing quantity of fish used as food 

 but also to the susceptibility of fish to decomposition, and to the 

 common arrangements on trawlers whereby the fish caught may remain 

 in an iced condition for from one to two weeks or longer, the detection 

 of the earlier stages of decomposition in fish is a matter of the highest 

 importance. 



Bearing on Public Health. — This appeals most to public health 

 authorities, whose concern is the public health, and especially to the 

 inspector of meat. His task of examining fish, for the purpose of 

 determining their condition and estimating their position between the 



