166 AN AMERICAN TEXT- BO OK OF PHYSIOLOGY. 



is more or less rapidly raised, at the same time that the changes in the length 

 of the muscle arc recorded on a slowly moving surface. Halliburton 1 gives 

 the following precipitation temperatures for muscle proteids. 



Name. Temperature of coagulation. 



Proteids obtained from i Paramyosinogen 47° C 



the dissolved clot . . I Myosinogen 56° C 



Proteids obtained from f Myoglobin 63° C. 



muscle-serum ... Myo-albumin 73° C. 



I Mvo-albumose (not coagulated by heat). 



Constituents of Muscle-serum. — Proteids. — The fluid which can be 

 expressed from the coagulated fresh muscle is called muscle-plasma, This 

 undergoes a change in the process of coagulation, two of the globulins 

 present, the para -myosinogen and the myosinogen, being precipitated in the 

 form of myosin, which makes the substance of the clot. The fluid which 

 .an be expressed from the clotted muscle, the muscle-serum, therefore lacks 

 at least two of the protcid constituents of the normal muscle. The proteids 

 of the muscle-serum are : myoglobulin, myo-albumin, and mvo-albumose. 



The myoglobulin resembles serum-globulin, although precipitated at 63° 

 C. instead of 78° C. The myo-albumin is apparently identical with serum- 

 albumin. 



To these proteids we must add the pigment haemoglobin. Another pig- 

 ment, myolncniatin, is also found. It is not unlikely that these pigments have 

 here as elsewhere a respiratory function. 



Although the proteids form the larger part of the solids of the muscle- 

 substance, but little is known as to the form in which they exist in the living 

 muscle or the part that they play in its activity. They seem to have a two- 

 fold function, they are at once the machine and the fuel. 2 Under normal 

 conditions they probably supply but a small part of the energy set free by 

 the muscle during ordinary work. In excessive muscular work they undergo 

 katabolic change, as is shown by the increased excretion of nitrogen and sul- 

 phur in the urine. In the case of an individual not in training it would 

 appear that during excessive muscular exercise, as in starvation, other parts 

 of the body may give up their proteids to the muscles, for under such cir- 

 cumstances uric acid and phosphorus-holding extractives, the waste products 

 of nuelein, appear in the urine, and the muscle contains but little nuclein. 3 

 This is much less the case if the individual is in training, from which it 

 would appear that through training muscles acquire the capacity of storing 

 more proteid <>r of utilizing their stock to better advantage. In any case if 

 a large amount of muscular work is to be done the amount of proteid in the 

 food should be increased. 



Nitrogenous Extractives. — The chief nitrogenous extractive is creatin ; in 



'Halliburton: Physiological Chemistry, p. 414. 



'Pfliiger: Pfluger's Archiv, 1899, lid. lxxvii. S. 425. 



3 Dunlop, Paton, Stockman, Maccadam: Journal of Physiology, 1897, xxii. p. 67. 



