470 PEACTICAL PHYSIOLOGY 



Place 50 c.c. urine in a round bottom J litre flask A, add 20 grains 

 sodium chloride to prevent decomposition and 50 c.c. methyl alcohol 

 to reduce the boiling point of the mixture. In flask B place 50 c.c. 

 or less Ti/10 acid and in G 10 c.c n/10 acid, diluted in both cases with 

 a little water. The flasks may be tilted obliquely and should be large 

 enough to prevent loss of acid by jumping over during the violent 

 commotion which is set up by the rapid passage of steam. If such 

 loss should occur, the acid may be recovered by rinsing out the flask D. 

 When the apparatus is ready, 1 gram of dry sodium carbonate is 

 added to the liquid in flask A, the stopper is rapidly inserted and 

 the suction started. The pump will quickly reduce the pressure to 

 about 30 mm. and the liquid in A, which is warmed up to about 

 40 C. in a water-bath, will begin to boil. The temperature of the 

 bath must be maintained and should not be allowed to rise above 

 50 C. for fear of decomposing urea. When the boiling has continued 

 for fifteen minutes, all the ammonia will have been given off and the 

 operation is stopped by slowly letting in air by the stopcock a. The 

 acid in B and C is titrated, after a few drops of a 1 per cent, solution 

 of Alizarin red have been added as the indicator. 



Variations in Amount Excreted. While discussing the metabolism 

 of urea, it will be remembered that one of its chief precursors is 

 ammonium salts. This fact would lead us to expect that the adminis- 

 tration of those salts by the mouth would be followed by an increase 

 in the amount of urea excreted. This is found, however, not to be the 

 case with all the salts of ammonia, but only with those in which the 

 acid radicle present is easily dislodged ; whereas in those salts, such as 

 chlorides, in which the acid radicle is very firmly attached, there is no 

 increased excretion of urea, but instead of this an increased excretion 

 of ammonia. It must be pointed out, however, that this statement 

 regarding ammonium chloride is true only in the case of carnivorous 

 and omnivorous animals. In the case of herbivorous animals, there 

 are so many strong bases taken with the food that the ammonium 

 chloride at once undergoes double decomposition in the tissues, the 

 chlorine combining with sodium to form sodium chloride, and the 

 ammonium combining with carbonic acid to form ammonium carbonate, 

 which becomes at once transformed into urea. The administration of 

 ammonium chloride to rabbits along with their ordinary food has, 

 therefore, no effect on the excretion of ammonia, but causes that of 

 urea to rise; but if the rabbit be starved, i.e. be caused to live on 

 its own tissues, then an immediate increase in the ammonia excretion 

 follows the administration of this salt, and the urea excretion remaina 

 unchanged. 



