ioo THE CHEMISTRY OF THE TISSUES AND ORGANS. 
creatine, creatinine, xanthine, hypoxanthine, carnine, carnic acid, uric 
acid, urea, taurine, and inosinic acid, (b) Non-nitrogenous, namely, fats, 
glycogen, inosite, dextrose, and lactic acids. 
Creatine and creatinine. — Creatine can be crystallised out by 
evaporating aqueous extracts 
of meat from which proteids 
and salts have been previously 
removed : on heating it with 
mineral acids it is converted 
into creatinine. The relation- 
ship of these two substances 
is shown by the following 
equation : — 
C 4 H 9 N ? 2 — H 2 = C 4 H ? N 3 
(creatine) (creatinine) 
According to Yoit, 1 the 
quantity of creatine in the 
voluntary muscles varies from 
0-2 to 0-3 per cent. This 
increases during starvation. 2 
Involuntary (cardiac and plain) contains less than voluntary muscle. 3 
The compound with zinc chloride which creatinine forms (Fig. 15) has 
been genera] ly used for isolating it from urine, and other places where it 
i (ccurs. My i iwn experience with 
,- 
5 
Fig. 13. — Creatine crystals. — After Kiihne. 
Fig. 14.— Creatinine crystals. — After Kiilnie. 
this method has shown that for 
quantitative purposes it is most 
uncertain ; and this no doubt ac- 
counts for the different results 
obtained by different observers. 
Thus Neubauer denies the exist- 
ence of creatinine in muscle 
altogether ; Voit, Sarokin, 4 and 
Monari 5 say that it increases 
during muscular activity, while 
NawrocM 6 states that it does 
not. Much more certain results 
are obtained by the use of (J. S. 
Johnson's method, in which he 
precipitates the creatinine as a 
compound of mercury. 7 This 
method, which has received the 
powerful recommendation of Hoppe-Seyler, s may be used to identify 
creatinine when it is present in very small quantities, as in the blood. 9 
The microscopic appearance of the precipitate is shown in Fig. 1G. By 
1 Ztschr.f. Biol., Miinchen, Bd. iv. S. 77. 
2 Demant, ZtscKr. f. physiol. Clicm., Strassburg, Bd. iii. S. 387. 
3 Voit. loc. cit. ; Lehmann, " Lehrbuch, " Bd. iii. S. 73. 
4 Virchow's Archiv, Bd. xxvii. 5 Ga-.:. chim. ital., vol. xvii. p. 367. 
8 CeiUraZbl.f. d. vied. Wisscnscli., Berlin, 1865, S. 417. 
7 Proc. Soy. Soc. London, vol. xlii. p. 365 : xlii. p. 493 ; 1. p. 28. Johnson 
here points out that there are several isomeric varieties of creatinine, differing in reducing 
power, etc. In his process he is careful to employ no heat; otherwise the creatinine is 
transformed into a non-reducing variety, or even may be changed into creatine. 
8 "Handbuch. d. physiol. chem. Analyse," 1893, 7th edition, S. 142. 
a Colls, Journ. Physiol, Cambridge and London, 1896, vol. xx. p. 107. 
