of the Fishery Board for Scotland. 



169 



Histological Structure. — On making a transverse section of a whiting 

 or haddock across the mesial lateral line, so as to include the red 

 muscle at its thickest part, and also the pale muscles, a low- 

 power view reveals the appearance seen in Plate V., fig. 11, 

 where F is the subcutaneous fascia investing the muscle, and sending 

 a well-marked septum S to the vertebral column V C. Other 

 concentric septa, S S S, separate the muscular fibres into lamellae. 

 It will be seen at once that there are two kinds of muscular fibres — one 

 (the red) lying under the fascia, and continued as a thinner layer inwards 

 to the vertebral column, and the other forming the great mass of the 

 laminae — the pale white muscles. On transverse section the red muscle (R) 

 appears darker, and its sectional area is smaller than the pale fibres, which 

 are thicker fibres altogether (P). In this respect they correspond to the 

 red muscles of the rabbit. There is no difficulty in separating the groups 

 of red fibres from the pale ones. All are supported by a certain amount of 

 connective tissue — the septa playing the part of a perimysium, from 

 which fibres proceed as a sustentacular endomysium. 



The sharp distinction between these two kinds of muscle is far better 

 marked in the mackerel. In a transverse section the red muscles are 

 seen lying in a depression of the pale ones, and accurately mapped off 

 from the latter by a septum. The red fibres are much smaller than the 

 pale ones. Between the large pale fibres are many fat-cells, forming a 

 nearly continuous network between the fibres, while this exists to a much 

 less degree in the area of the red muscles. It is very probable that the 

 condition of these fat-cells varies at difi'erent periods of the year. 



If one of the red muscles of a whiting or mackerel be teased out so as 

 to isolate a muscular fibre, on examining it with an ordinary power of 

 the microscope, it is seen to be transversely striated, but the striae may 

 not be very marked, and nuclei are seen with difficulty. What is very 

 remarkable, however, is the existence in the substance of the sarcous 

 matter of rows of small, bright, refractive granules, in some fibres assuming 

 a more or less longitudinal course, three, four, or more rows, being found 

 abreast in a fibre. (Plate V., fig. 7.) In others the granules may be 

 more densely packed, and assume a more transverse direction. All the 

 red fibres are not equally granular — some being more so, others less. The 

 small granules are undoubtedly fatty in their nature, for, apart altogether 

 from their optical characters, they are soluble in ether, and are blackened 

 by osmic acid. When ether is added they disappear, and the fibre 

 assumes the appearance of a transversely striated fibre. A transverse 

 section of such fibres is particularly instructive (Plate V., fig. 8), for we 

 see the polygonal shape of the fibres, and note that the granules lie in 

 the substance of the sarcous matter. It is no uncommon thing to meet 

 with granules in the substance of muscle. In the muscles of some insects 

 they are particularly well marked, but in these cases they are not fatty 

 in their nature. They are spoken of as 'interstitial granules.' Flogel 

 has described the existence of granules in the muscles of insects, and 

 Biedermann"^ has shown that they occur in the fibrillae of the thoracic 

 muscles of the humble-bee. These granules differ both in their position 

 in the sarcous substance and in their chemical nature, from those found 

 in the red muscles of fishes. It has been shown that section of the vagi 

 in the neck of a pigeon results in death of the animal, under conditions 

 quite different from those that obtain in a mammal. Section of the vagi 

 in the neck of a rabbit is followed by pneumonia and death within a 

 limited period. In a bird — e.g., pigeon — death also takes place, but there 



* Zur Lehre v, Bau d. quergest. Muskelfaser, Sitzb. d. K. Akad. d. Wiss. zu Wien, 

 Ixxiv. 



