ANIMAL FLUIDS AND TISSUES. 667 



prisms ; the solution is slightly alkaline to litmus. Creatinine is a 

 strong base, forming well-defined salts ; it also forms an insoluble 

 double compound with zinc chloride, for which reason the latter is 

 often used to precipitate creatinine. The occurrence of creatinine 

 in urine will be considered later. 



Experiment 77. a. Preparation of creatine. Digest 400 grammes of finely 

 divided lean beef with 500 c.c. of water at a temperature of 50 C. (122 F.) ; 

 filter the mass through cloth, press out well, and repeat the operation twice 

 with 1000 c.c. of water, bringing the mixture to the boiling-point each time ; 

 then evaporate the mixed filtrates to about one liter. (In place of the liquid 

 extract, thus obtained, a solution of commercial extract of beef may be used.) 

 Acidify the solution with acetic acid, heat to boiling, and filter off the coagu- 

 lated proteins ; to the cold filtrate add basic lead acetate as long as a precipitate 

 is formed, filter and precipitate excess of lead by passing hydrogen sulphide 

 through the solution. Finally filter, evaporate filtrate over a water-bath to a 

 syrup, and set aside. After a day or two crystals of creatine will be found, 

 which, if too highly colored, may be redissolved in water, decolorized with 

 bone-black, and recry stall ized. 



b. Conversion of creatine into creatinine. Heat 0.5 gramme of creatine with 

 10 c.c. of dilute sulphuric acid for half an hour over a water-bath ; then dilute 

 with 25 c.c. of water and add a sufficient quantity of powdered barium car- 

 bonate to neutralize the acid. Next filter, evaporate the filtrate to about 5 c.c., 

 and use this solution of creatinine for the following tests : 



1. To a few drops of the solution add an equal volume of an alcoholic solu- 

 tion of zinc chloride. Creatinine zinc chloride, (C 4 H 7 N 3 O) 2 .ZnCl a , crystallizes 

 in warty lumps, composed of fine needles or prisms. 



2. Weyl's reaction. Add, drop by drop, a freshly prepared, dilute solution 

 of sodium nitroprusside, Na 2 Fe(CN) 5 lS T O, until the solution is colored yellow; 

 then add drop by drop a dilute solution of sodium hydroxide : a fine transient 

 ruby-red color is obtained which soon passes into yellow. Acidulate solution 

 with acetic acid and warm : solution turns green, then blue, the color being 

 due to the formation of Prussian blue. 



3. To a very dilute solution of creatine add a trace of an aqueous solution 

 of picric acid and render faintly alkaline: the solution turns intensely red. 



Xanthine bases are a group of nitrogenous substances produced in 

 the organism as the result of the cleavage of nucleins. They are 

 closely related to one another, as also to uric acid, from which they 

 may be obtained by synthetic processes. Indeed, an increased secre- 

 tion of uric acid follows their ingestion as food. While eleven 

 xanthine bases have been isolated from the cell, only four (xanthine, 

 hypoxanthine, guanine, and adenine) are found in the muscle. Con- 

 jointly the xanthine bases are also termed alloxur bases or purine 

 bases. The first named refers to the fact that the nucleus of xanthine 

 bases is assumed to be made up of the carbon-nitrogen nuclei of 

 alloxsm, C 4 H 2 N 2 O 4 (an oxidation-product of uric acid), and wea, 



