PROXIMATE CONSTITUENTS OF THE BODY. 75 



the crystallizable substances formerly confounded under the title, may 

 now be reckoned creatin and creatmin, both of which exist in the 

 juice of muscle and in the blood. The latter is also found in the renal 

 excretion or urine, whilst the former occurs in the brain. Another 

 substance, named sarcin, sarcosin, or Tiypoxanthin, is also found in 

 the flesh and the blood. Xanthin occurs probably in all the soft 

 tissues, and in the urine ; it is allied to guanin. Leucin is another 

 of these compounds, supposed to be the products of metamorphoses of 

 albumen, and present in minute quantity in the body generally. 

 Tyrosin occurs only in disease. 



Amongst the azotized substances occurring in parts of the body 

 only, must be mentioned one, named cerebric acid, which exists in the 

 gray substance of the brain ; and also the cholic or glycocholic, and 

 the taurocholic acids, which are ingredients of the bile. These acids 

 break up respectively, into cholalic acid and glycocoll or glycocin, 

 and the same acid and taurin. Lastly, in the renal excretion, there 

 are found large quantities of the substances called urea and uric acid, 

 minute traces of which occur in the blood and soft tissues generally. 

 Urea is a white crystallized substance, exceedingly soluble in water, 

 to which it imparts a saline taste. It is remarkable that, though a 

 product of living animals, it can be made artificially from organic 

 matter, and is then known as a cyanate of ammonia, that is, a salt 

 consisting of cyanic acid and ammonia. It acts as a base itself, how- 

 ever, and is capable of uniting with acids to form highly compound 

 salts. Uric acid, normally existing in a state of solution in combina- 

 tion with ammonia or other bases, is easily precipitated in the form 

 of minute crystals, and then is very insoluble. It constitutes the most 

 common form of gravel and stone (hence its other name lithic acid, 

 from XiOos, lithos, a stone), and is even excreted in a semi-solid form 

 in birds, and in a solid form in serpents. Hippuric acid is said also to 

 occur in human blood and urine; it exists largely in the urine of her- 

 bivorous quadrupeds. 



Non-azotized Substances. Of these, by far the most abundant are 

 the various fatty matters, which are all distinguished by being insolu- 

 ble in water, but soluble in pure hot alcohol and in ether. The prin- 

 cipal seat of these fats is, of course, the adipose tissue ; but fatty mat- 

 ters are found also in the brain and in muscle, in the blood, and espe- 

 cially in the chyle. The fat of the human body consists chiefly of 

 olein, with a little so-called margarin dissolved in it. Olein is a fluid 

 fat or oil, similar to that which constitutes the basis of olive, and some 

 other oils. By being boiled with an alkali, as in the manufacture of 

 soap, olein is separated into a fatty acid, called oleic acid, and a sweet 

 viscid substance called glycerin, which of late years has become so 

 familiar to all. Palmitin is a solid crystallizable fat, which is decom- 

 posable into palmitic acid and glycerin. In the fat of the sheep and 

 ox, there is a third still more solid fat, stearin, which may be sepa- 

 rated into glycerin and stearic acid. Margarin, another solid fat, is 

 now supposed to be a mixture of stearin and palmitin. A fourth fatty 

 substance, found in the brain, is named lecithin. Margarin melts at 



