52 MATERIAL COMPOSITION OF MAN. 



composition of the gelatinous tissues ; but, as Dr. Carpenter has re- 

 marked, 1 there seems to be no valid reason thus to limit the mode- of its 

 production. 



9. Uric or litMc acid. This acid is found in the urine of man, birds, 

 serpents, tortoises, crocodiles, lizards; in the excrements of the silk- 

 worm, and very frequently in urinary calculi. It is obtained by dis- 

 solving any urinary calculus which contains it, or the sediment of hu- 

 man urine, in warm liquid potassa, and precipitating the uric acid by 

 the chlorohydric. Pure uric acid is white, tasteless, and inodorous. It 

 is insoluble in alcohol, and is dissolved very sparingly by cold or hot 

 water, requiring about 10,000 times its weight of that fluid, at 60 of 

 Fahrenheit, for solution. According to Dr. Prout, this acid is not free, 

 but is commonly combined with ammonia; the reddening of litmus 

 paper being not altogether owing to it, but to the super-phosphate of 

 ammonia, which is likewise present in urine. 



In the herbivora, this acid is replaced by the hippuric. Xqnthic 

 acid, found by* Marcet in urinary calculi, seems to have been uric 

 acid. 



10. Red colouring principles of the blood. It has been already ob- 

 served that Engelhart and Rose, German chemists, had detected iron 

 in the red corpuscles of the blood, but had not found it in the other 

 principles of that fluid. It has been considered probable, therefore, 

 that it has something to do with the colour. Engelhart's experiments 

 did not, however, determine the manner in which it acts, nor in what state 

 it exists in the blood. The sulphocyanic acid which is found in the 

 saliva, forms, with peroxide of iron, a colour exactly like that of venous 

 blood; and it is possible, that the colouring matter may be a sulpho- 

 cyanate of iron. 



To obtain the red colouring matter, hsematin or hsematosin, allow 

 the crassamentum or clot, cut into thin pieces, to drain as much as 

 possible on bibulous paper, triturating it with water, and then evapo- 

 rating the solution at a temperature not exceeding 122 of Fahren- 

 heit. When thus prepared, the colouring particles are no longer of 

 a bright red colour, and their nature is somewhat modified, in conse- 

 quence of which they are insoluble in water. When half dried, they 

 form a brownish-red, granular, friable mass; and, when completely 

 dried at a temperature between 167 and 190, the mass is tough, 

 hard, and brilliant. The mode in which the hsematosin is concerned 

 in the coloration of the blood, will be inquired into under the head of 

 RESPIRATION. 



A brown colouring matter, hvemaphsein, and a blue colouring matter, 

 hsemacyanin, have been described. The former, however, it has been 

 suggested, is nothing more than haematin modified by an alkali ; and 

 Simon 2 never succeeded in detecting the latter. 



11. Yellow colouring principle of the bile; cholepyrrhin of Berze- 

 lius, biliphsein of Simon. This substance is present in the bile of 

 nearly all animals. It enters into the composition of almost all gall- 

 stones, and is deposited in the gall-bladder under the form of magma. 



1 Human Physiology, 673, Lond. 1842. a Op. cit, p. 42. 



