352 PEACTICAL PHYSIOLOGY 



classes, (a) nitrogenous, (b) non-nitrogenous. The chief members of the 

 first group are creatin (C 4 H 9 N 3 2 ), and the purin bodies hypoxanthin 

 (C 5 H 4 N 4 0) and xanthin (C 5 H 4 N 4 2 ). The most important non- 

 nitrogenous extractive is sarcolactic acid (C 3 H C 3 ). 



Creatin is the most abundant extractive in muscle, amounting to 

 4 - -45 % in rabbits, -3 % in bullocks, '26 % in frogs, and -2 % in hedge- 

 hogs. Chemically it is closely related to urea, and can be changed 

 into this body and a substance called sarcosin by boiling with baryta 

 water. 



Creatin + Water = Urea + Sarcosin 



or, 



Although this reaction takes place outside the body, there is no 

 evidence that such is the fate of creatin in the body, although many 

 attempts have been made to prove that such is the case. Injection of 

 creatin into the body leads to no increase in the formation of urea of 

 the body. 



Another interesting relationship of creatin is to the substance called 

 creatinin. If creatin be boiled with dilute mineral acids it loses a 

 molecule of water and becomes changed into creatinin. 



y NH 



NH = C< 

 Ni 



CH 2 / 



Creatin - Water = Creatinin 



or, C 4 H 9 N 3 2 - H 2 = C 4 H 7 N 3 0. 



This reaction is the best means of recognising creatin, since it 

 gives no characteristic tests, whereas creatinin does. 



EXPERIMENT V. Take about 10 grammes of fresh muscle, grind 

 with alcohol, filter, evaporate at about 50 C. Dissolve in water and 

 divide into two equal portions, a and b. To a add 15 c.c. of saturated 

 picric acid solution and 5 c.c. of 10 % caustic soda. Allow to stand 

 5' and dilute to 500 c.c. Note that there is no change in the colour of 

 the solution, therefore creatinin is absent. To b add half its volume 

 of N . HC1 and heat in a flask fitted with a cork and glass tube to act 

 as air condenser on water-bath for five hours. Neutralise with caustic 

 soda, add picric acid solution and caustic soda, and dilute as before. 



