Report on Diseases and Abnormalities in Fishes. 29 



healed, and the fish was in a very fat condition, the injuries must 

 have been caused some months, at least, previously. The effect of 

 an external injury would then appear to remain a long time in the 

 muscles. The injury had been done, I believe, in fresh water. I 

 therefore examined a scale in order to find the ' ' spawning-mark " 

 described by Johnstone. I made out no such mark on the scale. 

 The fish was quite healthy, so far as I could judge. I examined 

 several of the nerves on the inside of the abdominal wall, but found 

 no trematode cysts. 



A cod showed a number of red regions scattered through the 

 whole of its flesh. They measured in greatest size about 6 mm. 

 The bloodvessels between the muscle fibres were swollen and flushed 

 with blood, and they gave the patch a dark-red colouration. There 

 were many red areas along the ribs. This condition is probably due 

 to mechanical injury before death. 



An interesting question is concerned with the cause of the 

 difference in colour between the muscles in different parts of the 

 fish. Many fishes have brown or red muscles along the side of the 

 body, near the lateral line, while the main mass of the muscles is 

 pale or colourless. Stirling says that in the haddock and whiting 

 the red muscle fibres, seen in a cross section made at the lateral line, 

 are smaller in diameter than the pale muscle fibres. " The red 

 muscle shows in the substance of the sarcous matter several rows of 

 bright refractive fatty granules, which in some fibres assume a more 

 or less longitudinal course." He further remarks that the red 

 muscle fibres present all the appearance of a muscle in a state of 

 fatty infiltration, or fatty degeneration. 



Mahalanobis, in discussing the fat in the flesh of the salmon, says 

 that the muscle is not correctly described as undergoing fatty 

 degeneration. The condition should be described as interfibrillarv 

 infiltration of fat. . . In all probability the muscle cells 

 absorbed fat and stored it between the fibrils. . . The loss of 

 transverse striation is parti} 7 due to the interfibrillary granules of 

 fat. 



If a piece of the brown muscle from the salmon be teazed out, the 

 fibres are found to have much more oil than those of the pink muscle. 

 There is also a greater collection of oil globules between the fibres 

 of the former. When a piece of the brown muscle is teazed out it 

 is bathed in a copious bath of the oil set free : the fibres separate 

 very readily. Under the microscope this fibre is much more opaque 

 than that of the pink muscle. Fig. 109 represents a red fibre as 

 seen with Obj. Oil immersion 2 mm. Oc. 4. The fibrillae are crowded 

 with comparatively large oil globules, which evidently distend their 

 sheaths. ^ The fibrillge, in consequence of the closely-packed globules 

 and their swollen condition, are more distinct than in the pink 

 muscle. The transverse striae were not made out in the brown 

 muscle fibre. 



The pink colouration of the flesh of the salmon would appear to 

 depend on the quantity of oil in the muscle fibre, and perhaps also 

 on the structure of the fibre. The oil itself is colourless. I do not 

 consider that the pink colouration of the muscle is due to pigment. 

 Newbigin, however, extracted two pigments, pink and yellow 

 respectively, from the muscles of the salmon. She considered the 

 pink colour of the flesh to be due to the presence of coloured fat. 



