34 



Appendices to Second Annual Report 



there are other figures of the structure of the herring in the Report of the 

 Commissioner for the United States' Commission on Fish and Fisheries 

 for 1879. The American Report is a translation of Heincke's paper on 

 the structure of the herring. 



• The most extensive experiments on the digestion of fishes is given by 

 Krukenberg.* 



Reaction of the Digestive Tract. — The digestive tract, more espe- 

 cially the oesophagus, crop, and stomach, are covered by a thick layer of 

 mucus, and, unless this be removed, one is •sometimes apt to mistake the 

 reaction of these parts of the canal. The reaction of the oesophagus I 

 have found to be neutral or alkaline, the mucous membrane of the gastric 

 sac is usually acid, although it sometimes is neutral or even alkaline 

 when a herring is examined with its cardiac and pyloric sacs empty, which 

 was very frequently the case during the period I subjected the herrings to 

 examination. During digestion the cardiac sac and its contents are always 

 acid. The mucous membrane of the pyloric sac, covered as it is with a 

 thick coating of mucus, is often alkaline on the surface during fasting, but 

 during digestion when it is filled with food, or if the mucus is removed 

 even during fasting, the mucous membrane has a distinctly acid reaction. 

 The contents of the pyloric cceca are distinctly alkaline, while the con- 

 tents of the gut, from where the pyloric caeca and bile duct pour their 

 secretion into the intestine, are alkaline as far as the anus. The liver is 

 alkaline in reaction, but it very soon becomes acid. The bile is feebly 

 alkaline or neutral. Those results agree with those that obtain in man 

 and mammals generally. 



In order to test the digestive properties of each part of the intestinal 

 canal, it is necessary to extract the various ferments (or enzymes) from 

 the mucous membrane in which they are formed, for one cannot obtain 

 sufficient of the digestive fluids themselves to experiment with. 



Methods. 



The methods I employed were those in use for the extraction of the 

 ferments present in the mammalian digestive tract. One of the best 

 solvents of those bodies is glycerine, and this I used extensively for 

 extracting such ferments as are soluble in it. Besides this, I also 

 extracted the mucous membrane with water, which removes the reserve 

 stock of the ferment, or at least the mother -substance of the ferment, stored 

 up within the cells which manufacture the ferments. I also subjected 

 some parts of the intestinal tract to the action of the fluids recommended 

 by Dr Wm. Roberts,f viz., a boracic solution, which contains 3 to 4 per 

 cent, of a mixture of boracic acid and 1 part of borax; dilute spirit, i.e., 

 water containing 10-12 per cent, of rectified spirit; chloroform water, 

 which consists of chloroform and water in the proportion of about 1 in 

 200. The advantage of using glycerine and these other 'extracting 

 ' reagents ' is, that a solution of the ferments is obtained which can be 

 kept for a length of time and still retains its digestive properties. Other 

 fluids were used for special purposes. 



It was no part of my purpose to investigate the different kinds of food 

 on which the herring feeds, but in opening the animals, necessarily a few 

 observations on this subject were forced upon one's attention. The con- 

 tents of the stomachs of herrings caught off the Aberdeenshire coast have 

 been subjected to an extremely minute and careful analysis by Mr George 

 Sim, and his results are to be found in his Natural History of the Herring. 

 In the herring which I examined, and which contained food, this food 



* Kiihne's Unteruchsungen, vol. i. 



t On the Digestive Ferments, by Wm. Roberts, M.D., 1880. 



