9 i8 METABOLISM. 
circulating fluid. The amount which is not accounted for may possibly 
pass into the constitution of the proteids and nucleo-proteids, and also 
of those albuminoids from which a carbohydrate material has been 
obtained on decomposition with acids, and it may be that the excess is 
in this way stored until required. In the embryo, glycogen is much 
more widely distributed and occurs in much larger proportion than 
after birth, especially in the developing muscles ; at this time the liver 
may contain very little. It occurs also in considerable amount in the 
placenta. 
The glycogen, both of the liver and of the muscles, gradually dis- 
appears in starvation, and first from the liver. 1 The disappearance is 
accelerated by muscular work, 2 and in warm-blooded animals by external 
cold ; 3 it is probable, therefore, that the glycogen is used for the pro- 
duction of both work and heat. The rate at which it disappears in 
starvation varies greatly in different animals. Aldehoff found it in large 
quantity in the muscles of a horse which had fasted for nine days ; 
in doo-s it may be found after three weeks, and has been detected 
after thirty-five days' fasting; 4 in rabbits it has disappeared usually 
within a week. In frogs it accumulates in the liver towards the 
end of the summer, and gradually disappears during the winter; 
but even if they take no food, there is still some present at the end 
of the winter, but more in the muscles than in the liver. The same 
is the case with hibernating animals (Voit). On the other hand, if 
carbohydrates are given to animals deprived of their glycogen by 
starvation, this substance very rapidly reappears in the muscles and 
liver. 5 
The diminution of the glycogen of the muscles, concomitantly with their 
activity, has been already referred to in connection with muscular metabolism 
(p. 915). In the passage of excised muscles into the condition of rigor mortis 
there is a certain amount of disappearance, amounting, according to Werther, 6 
to as much as 50 per cent, of the original amount, but far less than as the 
result of tetanising the muscles. In either case, what becomes of it is not 
clear ; the sarcolactic acid which makes its appearance is not derived from it ; 
the formation of the acid is not dependent upon the presence or absence of 
glycogen. If rigor is allowed to come on in the cold, the acid still appears, but 
thereis no appreciable disappearance of glycogen. 7 On cutting the nerve pro- 
ceeding to a muscle, the glycogen becomes increased in quantity. 8 The increase 
proceeds up to the fourth day. Section of the tendon of a muscle has a 
similar effect. 9 
According to the observations of Kiilz, glycogen begins to appear in the liver 
1 Aldehoff, Ztschr. f. Biol., Munchen, 1889, Bd. xxv. S. 137 ; Hergenhahn, ibid., 1890, 
Bd. xxvi. S. 225. 
2 Manche, Ztschr. f. Biol., Munchen, 1S89, Bd. xxv. S. 163. The glycogen of muscles 
disappears after a period of tetanus, and also in frogs poisoned by strychnia, but not in 
the muscles of a lesj the sciatic nerve of which has previously been cut. 
3 Kiilz, Arch.f. d. ges. Physiol., Bonn, 1881, Bd. xxiv. S. 46. In cold-blooded animals 
external warmth produces the disappearance of glycogen from the liver (Langley). 
4 Quinquand, Compt. rend. Soc. de biol., Paris, 1886, p. 285. 
5 For references, see Bun ge, "Lectures," pp. 383-385. See also Langley, Proc. Roy. 
Soc. London, 1882, vol. xxxiv. p. 22 (histological observations) ; Quinquand, Compt. rend. 
Soc. de biol., Paris, 1889, p. 285 ; Deweyre, ibid., 1892, No. 19. 
6 Arch. f. d. gcs. PJu/sioL, Bonn, 1890, Bd. xlvi. S. 63. 
7 Bbhm, ibid., 1880," Bd. xxiii. S. 44. 
8 Bernard, Compt. rend. Acad. d. sc, Paris, 1859, tome xlviii. p. 683. 
9 Boldt, Diss., Wurzburg, 1893; Vay, Arch. f. c.vpcr. Path. u. PharmakoL, Leipzig, 
1894, Bd. xxxiv. S. 45. 
