386 THE MUSCLE-TISSUE. 



other tissues and fluids of the body where nitrogen is also found, its 

 presence is probably of no significance. The quantity that can be 

 obtained by the vacuum pump is essentially the same as that which 

 is found in the lymph and in the blood. 



FAT. 



The amount of fat which is found in muscle-tissue varies not only 

 with different animals but also in one and the same individual at 

 different periods of life. Some of the analytical results which have 

 been obtained are shown below : 



Pro mille. 



Lean beef 6.1-7.6 



Rabbit 10.7 



Partridge 14.3 



Pig 40.0-90.0 



Salmon 100.0 



Mackerel 164.0 



Eel 329.0 



The fat is deposited not only in the interfibrillary connective 

 tissue, but also in the sarcoplasm proper, and is apparently more 

 abundant in the red meat, which contains more sarcoplasm than in 

 white meat. 



Like glycogen, it here represents a reserve source of muscular 

 energy, but is apparently utilized more especially when a sufficient 

 supply of the former or of grape-sugar, as such, is not available. 



While it is ordinarily derived from the ingested fats or from carbo- 

 hydrates, there can be no doubt that under certain pathological condi- 

 tions, which are associated with. an increased destruction of tissue 

 albumins, it can also originate from these. This question, however, 

 we shall not consider in detail at this place, but shall revert to it in 

 a future section. 



In addition to fats, muscle-tissue also contains a small amount of 

 cholesterin, fats, and fatty acids, and at times considerable quanti- 

 ties of lecithins (0.69 per cent.). 



The chemical composition of involuntary muscle-tissue is appar- 

 ently similar to that of the striped variety. From the muscles of 

 the stomach of the pig and goose Velichi obtained a spontaneously 

 coagulating plasma, from which one albumin was precipitated on 

 dialysis, while a second remained in solution. The first was solu- 

 ble in dilute solutions of the neutral salts and was precipitated by 

 acetic acid ; it coagulated between 54 and 60 C. The second 

 coagulated between 46 and 50 C. 



In the holothurians, which probably represent one of the lowest 

 forms of animal life in which an actual differentiation of proto- 

 plasm to muscle-tissue has occurred, the tissue is apparently of the 

 unstriped variety. In stictopus, which belongs to this order, 

 v. Fiirth was unable to isolate an albumin coagulating below 50 C., 

 while Krukenberg states that in the case of Holothuria tubulosa his 

 extraction liquid coagulated at 45 C. 



