14 



Part III. — Twenty -sixth Annual Report 



the putrefaction of fish, including a bacteriological study of the subject, 

 and the observations and experiments referred to below were in part made 

 at the Fishery Board's Marine Laboratory at the Bay of Nigg and partly 

 in the laboratories of Marischal College. 



The subject of the putrefaction of fish, it need scarcely be said, 

 concerns not only one of the chief sources of our food supply, but also the 

 interests of a great industry. Fish as a foodstuff has in recent years been 

 gradually gaining in favour, and by the great development of trawling 

 increased supplies have been made available both for use in the fresh 

 condition and for curing purposes. 



Cause of Decomposition. — Fresh fish from its essential nature is a 

 foodstuff which very readily undergoes decomposition and putrefaction ; 

 and it is now well understood, and capable of easy demonstration, that 

 these processes are associated with, and chiefly caused by, micro- 

 organisms which are universally present. It is also well known that the 

 three chief factors which facilitate or inhibit the action of the micro- 

 organisms are (1) the supply of nourishment, (2) the temperature, and 

 (3) the degree of moisture. 



Structure and Chemical Composition of Flesh of Fish. — Further, the 

 structure and chemical composition of the muscular tissue in fish are 

 such as to facilitate the easy invasion of bacteria and the early onset 

 of decomposition. With regard to the structure we find that in 

 mammals the red variety of striped muscle predominates, whereas in 

 fishes it is the pale variety that is general, and the latter exhibits a lower 

 grade of differentiation than the former. In pale muscle the striations 

 are less regular and the fibres much more readily break up into smaller 

 filaments, and these again into discs. The fibres are not so much bound 

 into separate and strong bundles as in the red muscle in mammals, those 

 which subserve locomotion being simply separated from each other by 

 delicate connective tissue septa. It may also be noted that pale muscle 

 is slightly less vascular than the red. 



When we consider the chemical composition of fish we find that the 

 various edible fishes differ less amongst themselves in composition 

 than do the meat foods. But it has to be noted that there is considerably 

 more refuse matter, such as skin and bones, in fish than in other flesh 

 foods, and that this refuse matter contains considerably less water, 

 proteids, fats, and salts than are found in the edible parts of fish. The 

 following table showing the composition of edible fish, beef, mutton, and 

 pork is compiled chiefly from the excellent works of Konig, Voit, and 

 from the Reports of the Massachusetts State Board of Health : — 



Water, . 



Proteids, 



Fats, 



Inorganic Salts, 



Approximate Percentage Composition of 



Edible Fish. 



Beef. 



Mutton. 



Pork. 



Mack- 

 erel. 



Had- 

 dock. 



Fat. 



Medi- 

 um. 



Lean. 



Fat. 



Lean. 



Fat. 



Lean. 



72 

 19 



8 



1-5 



82 

 17 



•3 

 1-5 



53 

 17 

 29 

 1 



72 

 21 

 6 

 1 



76 

 21 

 2 

 1 



53 

 17 

 29 

 1 



76 

 17 

 6 

 1 



47 

 15 

 37 

 1 



72 

 20 

 7 

 1 



