84 BULLETIN OF THE BUREAU OF FISHERIES. 



5. There is a considerable store of adipose fat in the myocomraata, in the adipose 

 tissue around the small longitudinal muscles in the mid-dorsal and mid-ventral lines, 

 and in the connective tissue of the skin. A slight amount of fat in the viscera should be 

 mentioned. 



PROTOCOLS. 



Male salmon (no. p7), length 2^.y cm., taken at Baird, Cal., July 18, 1911. 



This young salmon was caught with hook and line with salmon-egg bait from the deep pool opposite 

 the fish hatchery at Baird, Cal., July 18, 1911. It was a relatively large summer fish derived from the 

 last fall's hatch, as shown by the scale marks kindly identified for me by Prof. Charles H. Gilbert. It 

 was kept alive in a fish can for seven days, after which it was killed and examined for fat. On examina- 

 tion it was found that the testes were well developed, almost mature, and white in appearance. Speci- 

 mens of the alimentary tract and of the musculature were fixed in formalin for fat staining. Also 

 samples were preserved for paraffin sectioning. 



Microscopic examination of the trunk muscle/or stainable/at. — Samples of the lateral muscle preserved 

 in 10 per cent formalin were prepared after five months. Freezing microtome sections were stained for 

 fat with alkaline alcoholic scarlet red and coimterstained with haematoxylin. The fat was present 

 in the trunk dark muscle in large amounts and had not been extracted in any appreciable amount by 

 the long immersion in formalin. As the glycerin mounts were beginning to clear there was a stage of 

 verv sharp and distinct differentiation. The fat droplets in the body of the muscle were surrounded 

 or at least partially surrounded with rings of fibrillje.a The clear, brilliant scarlet red of the fat drop- 

 lets contrasted sharply with the palisade-like bands or rings of fibrillae. The sarcolemma at this stage 

 of clearing made a clearly marked line inclosing fat droplets between it and the fibrillar areas. These 

 latter fat drops are distinctly outside the areas of fibrillae, yet some of them press slightly into the 

 interfibrillar spaces. There is not much of this displacement of fibrillae for the reason that the superfi- 

 cial area of the salmon muscle fiber is bounded by a continuous band of fibrills. 



The fibrillae are strap-shaped, i. e., their outlines in cross section are rod-shaped. The fibrillae are 

 set witli their flat sides approximating each other and their narrow edges, therefore, bordering on the 

 surface of the fiber in the case of the superficial area. It is tliis that gives the palisade-like arrangement 

 in the superficial coat of the muscle. The continuity of the superficial band is occasionally slightly 

 interrupted, since the rows of fibrillae as seen in cross section here and there turn in toward the central 

 portion of the fiber. UTiere such turns come there is a slightly greater quantity of sarcoplasm present. 



Those dark muscle fibers n,earest the skin seem more loaded with fat, although the whole layer is 

 rather uniform in its loading. The striking thing about the material from this fish is the amount of fat 

 which is under the sarcolemma. In general, the fat droplets in this region are fairly uniform in size and 

 are spherical. But often a mass of fat seems compressed and spreads somewhat around the surface of 

 the fiber. Numerous instances are seen in which such masses of fat extend around one-sixth to one- 

 third the circumference of the fiber. If one gets a view of such a fiber isolated from the mass this type 

 of fat droplet or group of droplets stands out like a great blister on the side of the fiber. These droplets 

 are evidently compressed by the pressure of the sarcolemma. They no doubt exist within that sheath 

 under a certain amount of tension. 



The fat droplets within the substance of the fiber vary extremely in size and shape; the average 

 of the larger drops is about 4.5 to 6 ji. 



Through a typical section foiu- striking variations from the general picture appear. In each of 

 these an enormous fat drop has formed in the center of the muscle fiber. One of these fat drops measures 

 iS /! in diameter, while the fiber containing it measiu-es :^^ 11 in diameter. The thinnest part of the mus- 

 cular ring is 4 /i and tlie thickest S u. Evidently in this instance an enormous fat drop has formed in 

 the center of the fiber and crowded out the muscular substance into a superficial ring of protoplasm. 

 In this case the ring of protoplasm is filled as full of fat drops as plums in a pudding. There are thirteen 

 such droplets from 2 to 4 /t in thickness. There is not so much fat as usual between the sarcolemma and 

 the muscle substance. Four such fat drops are to be counted in one locality. In another region of the 

 section a fat cavity in the fiber measures 24 /< in thickness. The ring of protoplasm around it is not so 

 thick as in the preceding instance, and the fat drop itself has been pushed to one side, though it is still 

 adherent to the section. Smaller drops of fat are present in the ring of protoplasm. In yet another 



a Greene, C. W.: A new type of fat-storing muscle in the salmon, Oncorhynchus tschaw>-tscha. American Journal of 

 Anatomy, vol. 13, 1912, fig- i. pl. i. 



