of the Fishery Board for Scotland. 



225 



Taken as a whole, however, the results obtained by Chittenden and 

 Cummins seem to show that all fish are much less digestible than beef. 

 This result is to some extent, at all events, explained by one reason which 

 they give for adopting the above somewhat complicated method of ascer- 

 taining the amount of material digested. The simplest method is of 

 course to weigh the residue left on the filter, and by comparing this with 

 the weight of the flesh before digestion to ascertain the amount which 

 has been dissolved. They did not adopt this method because 1 the 

 ' undissolved residue of the fish is so gelatinous that it is next to an 

 1 impossibility to wash it entirely free from peptones.' If the new 

 method be adopted no attempt can be made to wash the peptones from the 

 residue, a considerable proportion of them must be left adhering to it, and 

 the digestibility of fish tested by this method must of necessity be lowered. 



In this relation it is interesting to refer to a paper by Professor Stirling* 

 on the red and white muscles of fish, in which he shows that most white 

 fish have two kinds of muscles : — first, the ordinary white muscle arranged 

 in myotomes, which when deprived of its blood is quite white ; second, 

 a band of red muscular fibres generally arranged in connection with the 

 lateral line, which retains a yellow or yellowish-red colour even when all 

 the blood has been washed out by careful injection of a half per cent, salt 

 solution. This colour is in the sarcous substance itself; and is due to the 

 same cause as that of blood, namely the presence of haemoglobin. Similar 

 differences in the flesh of other animals have long been known. Thus 

 everyone is familiar with the fact that the muscles on the breast of a 

 chicken, are, after boiling, much whiter than those of the limbs. There 

 is a considerable difference in the nutritive value of the two, as is shown by 

 some of Chittenden and Cummins' experiments. Thus 20 grammes of the 

 light meat of the shad (Clupea sapidissima) was found after digestion by 

 the method described above to have yielded 3*9352 grammes of peptones 

 and salts in a state of solution ; 20 grammes of the dark meat of the same fish 

 only yielded 3*5332 grammes. The difference in the case of chicken was 

 much less striking ; but 20 grammes of the light meat of that animal yielded 

 3 '509 grammes of nutritive material in solution, while 20 grammes of the 

 dark meat only yielded 3*4160 grammes. These figures were compared 

 with the amount digested from 20 grammes of beef, which was taken as 

 100. The result was that the light meat of the shad was as 97, while the 

 dark meat was as 87. The proportion in the case of chicken proved to 

 be, light meat 86*72, dark meat 84*42. 



The cause of this difference is at first not very easy to see, for the 

 amount of solid matter in the dark muscle of the shad is 32*63 per cent., 

 while in the light muscle it is only 20*38 per cent. In the dark muscle 

 of the chicken the percentage of solid matter is 26*70, in the light muscle 

 it is 26*64. From these figures one would a priori expect the red muscle 

 to furnish a larger supply of nutritive material than the white. But, as 

 pointed out above, it is not merely the amount of solid matter in a given 

 sample that determines the amount which may be digested from that 

 sample, and in the case of beef the more solid matter there is present the 

 Jess is the amount of proteids. This would seem also to be the case with 

 the red muscles of fish, for Professor Stirling observed that in the 

 muscular fibres there are numbers of minute, bright, highly refractile 

 globules, which are dissolved by ether, and blackened by osmic acid, and 

 therefore undoubtedly fatty in their nature. Fat is not only unacted on 

 by digestive fluids, but has long been thought to diminish their action 

 on proteids with which it is associated. Thus Voit remarks that ' the 

 ' digestibility is probably in part dependent on the nature of the fat present 

 "Report of Scotch Fishery Board for 1885, Appendix F, No. IX, 

 2 F 



