108 Investigations on the Li fc- History 



thickness in the case of fish leaving the sea early in the year ; whereas 

 towards the end of summer and in autumn I find an average of -^min. 

 thick. For the amount of fat in the endami/sixm, as well as the iiitra 

 cellular fat, we must depend on osmic acid preparations. 



B. THOSE FIXED WITH OSMIC ACID. 



J . Fat between Muscle Fibres. In fish coming from the sea there is 

 an abundance of fat cells between the muscle fibres, but in fish that have 

 been for some time in the r,ver this fat has almost entirely disappeared. 

 Fig. 4 is from an upper-water fish, hence even in this longitudinal 

 section we notice a marked absence of intercellular fat, whereas Fig. 5, 

 being from No. 79 (a fish fresh from the sea), shows, even in the trans 

 verse .section, presence of abundance of fat. 



2. Fat Inside the Muscle Fibres. Treatment with osinic acid ex- 

 plained the cause of longitudinal cleavages in the muscle fibres, and 

 revealed the presence of tine granules of fat along the cleavage lines 

 between bundles of fibrils, also between individual fibrils (Fig. 1). 

 In transverse sections also these granules can be seen lodged between 

 the fibrils. (Fig 2.) 



To make sure that these iiiterjibrillary granules of fat were not just 

 small particles broken up from connective tissue-fat and scattered over 

 the sections during washing, etc., every slide, during the whole process, 

 was kept in a vertical position with a marked end always upward ; so 

 that all flow of particles, if there were any, would be in one direction 

 only ; but the specimens show a very uniform distribution of these 

 granules. 



The amount of this intracelhdar fat varies very much at different 

 periods. In early fish the amount is much greater and the granules 

 much larger than in late fish. 



In the fish leaving the sea this accumulation of fat in the fibres 

 sometimes reaches an enormous amount, and a thick layer occurs under 

 the sarcolemma. This will be evident from a comparison between Fig. 

 2 and Fig. 3, the former being from a late fish, 69, and the latter 

 from No. 79. 



Chemical analyses showed the amount of fat in these fish to lie, in per 

 cent : 



Thick. Thin. 



G9 3-7 6-6 



79 12-6 20-2 



Summing up the results of the examination of the specimens fixed in 

 corrosive sublimate and of the corresponding ones in osmic acid, we 

 find that the evidence of the microscope tallies with the result of the 

 chemical examination, and points not only to a change in the amount, 

 of muscle fat, but also, to some extent, in the nature of its distribution, 

 at different periods. The early fish at the mouth of the river have a 

 much greater amount of fat in the muscles (both intercellular and 

 intracellular) than the late fish in the upper rea< lies. 



This diminution of muscle fat in the late fish may be due to a want of 

 fresh accumulation or to an increasingly active removal. But the 

 enormous difference in amount between a fish like No. 72 or No. 79 

 and one that is about to spawn, cannot be accounted for by either of 

 these causes singly. There is, no doubt, more active removal of fat- 

 probably slightly due to increased amount of work in going up the 

 river but mainly due to an export to the generative organs. A fish 

 like No. 79 has a very small ovary and large amount of muscle, 

 whereas a fish about to spawn has a very large ovary and small amount 

 of muscle. This obviously points to the fact that in the late fish the 

 ovary grows at the expense of the muscles. At the same time, it is 

 evident that if during the growth and development of the sexual 



