THE XANTHIN-EASES. 363 



boiled so as to remove coagulable albumins. The filtrate is pre- 

 cipitated with subacetate of lead, care being taken to avoid an 

 excess. The resulting filtrate is treed from lead by hydrogen sul- 

 phide, and is concentrated to a small volume at as low a temperature 

 as possible. On standing, the kreatiu crystallizes out, and can then 

 be purified as desired. To identify the substance, it is conveniently 

 transformed into kreatinin by prolonged boiling (one-half to one 

 hour) with dilute hydrochloric acid. The resulting material is then 

 examined as described in the section on the Urine (page 246). 



In addition to the common kreatins which have just been con- 

 sidered, Gautier succeeded in further isolating xanthokreatinin, 

 crusokreatinin and amphykreatin from muscle-tissue. The sub- 

 stances are, however, found only in traces and have not as yet been 

 studied in detail. 



THE XANTHIN-BASES. 



The xanthin-bases which have been isolated from muscle-tissue 

 comprise xanthin, hypoxanthin, and guanin. In addition, an- 

 other basic substance has been obtained, which is termed carnin. 

 This is manifestly closely related to the xan thins proper, as on 

 oxidation it is transformed into hypoxanthin. These bodies are 

 formed during the metabolism of the muscle nuclei, and are in part 

 eliminated in the urine as such. A variable fraction, however, is 

 directly oxidized to uric acid, which in turn may contribute to the 

 formation of urea, but is in part also eliminated directly (see pages 

 222 and 233). 



Isolation. To demonstrate the presence of the xanthin bases in 

 muscle-tissue it is necessary to work with large amounts of material, 

 as the quantity present is always small. On the whole it is more 

 convenient to start with some extract of beef, such as that of Liebig, 

 and to proceed as follows : 



The material in question is taken up with an amount of water 

 which is just sufficient for its solution, at a temperature of about 

 50 C. The liquid is then precipitated with a solution of sub- 

 acetate of lead. The resulting filtrate we term A. The pre- 

 cipitate contains the carnin in combination with lead. To isolate 

 the substance the mass is suspended in water and boiled. The 

 filtrate while still hot is saturated with hydrogen sulphide, which 

 decomposes the lead compouncl of carnin with the liberation of the 

 free base. The lead sulphide is filtered off, the filtrate concen- 

 trated to a small volume and precipitated with a concentrated 

 solution of silver nitrate. Ammonia is added to dissolve any pre- 

 cipitated chlorides when the insoluble silver-carnin is placed in 

 a small amount of hot w r ater and is decomposed with hydrogen 

 sulphide. The solution is filtered while hot, decolorized with 

 animal charcoal, and precipitated with alcohol. The carnin is thus 

 thrown down. 



