MUSCLE 667 



There is more water in the muscles of young than of old animals 

 (v. Bibra), and more in tetanized than in rested muscle (Ranke). 

 The fats belong to a small extent to the actual muscle-fibres. For 

 even when the visible fat is separated with the utmost care, nearly 

 i per cent, of fat still remains (Steil). 



The glycogen content varies extremely in different muscles and 

 in the same muscle under different nutritive and functional con- 

 ditions. Thus, in one and the same dog the biceps brachii contained 

 0*17 and the quadriceps femoris 0^53 per cent. In dogs on a diet 

 rich in carbo-hydrate and protein the percentage in the whole 

 skeletal musculature ranged from 0-7 to 3-7, and in the heart from 

 o'i to i -2. The average for human muscles has been given as 

 0*4 per cent. In lean horse-flesh Pfliiger found 0*35 per cent, of 

 glycogen, but no sugar. The total nitrogen was 3' 21 per cent, of 

 the moist tissue. The lactic acid of muscle and other tissues is 

 the ^-lactic acid, which rotates the plane of polarization to the 

 right. By the action of certain bacteria on cane-sugar /-lactic 

 acid is obtained, which is left rotatory. The optically inactive 

 fermentation lactic acid is obtained by the fermentation of lactose. 



Smooth muscle is somewhat richer in water than the striated 

 variety from the same species, because skeletal muscle is richer in 

 fat. Glycogen is either absent or present only in traces in the 

 smooth muscle (of the stomach and bladder). Lactic acid, kreatin, 

 and kreatinin are also found in much smaller amount than in striped 

 muscle (Mendel and Saiki). As in striated muscle, hypoxanthin is 

 the conspicuous purin base occurring in the free form i.e., obtain- 

 able in muscle extracts. The most remarkable difference in the 

 quantitative relations of the inorganic constituents is that in 

 striated muscle potassium preponderates over sodium and mag- 

 nesium over calcium, whereas in the smooth variety this relation 

 is reversed. 



It would be natural to expect that the proteins, which bulk 

 so largely among the solids of the dead muscle, and which are 

 so obviously important in the living muscle, should be affected 

 by contraction. But up to the present time no quantitative 

 difference in the proteins of resting and exhausted muscle has 

 ever been made out. The quantity of kreatin (and kreatinin) is 

 said by some authorities to be increased. The following chemical 

 changes have been definitely established. In an active muscle 



(a) More carbon dioxide is produced. 



(b) More oxygen is consumed. 



(c) Lactic acid is formed. 



(d) Glycogen is used up. 



(e) The substances soluble in water diminish in amount ; those 



soluble in alcohol increase. 



That the carbon dioxide is not formed by direct oxidation, 

 but by the splitting up of a substance or substances with which 

 the oxygen has previously combined, is, as has already been 

 shown (pp. 261, 263), highly probable. 



Formation of Lactic Acid Reaction of Muscle. To litmus- 

 paper fresh muscle is amphicroic that is, it turns red litmus blue 

 and blue litmus red. This is due, partly at least, to the phosphates. 

 Monophosphate (tribasic phosphoric acid, H 3 PO 4 , in which one 



