310 PHYSIOLOGY AT THE FARM. 



Isinglass obtained from the inner membrane of the swimming 

 bladder of the sturgeon is a good type of gelatine ; glue is an 

 impure form of gelatine ; size prepared from parchment is an- 

 other commercial form of gelatine. Patent gelatine is prepared 

 with more care than glue from the ligamentous parts of animals. 



Chondrine is prepared by boiling the cornea of the eye or 

 any of the permanent cartilages ; it is obtained also from the 

 primary cartilages before ossification takes place. When a 

 permanent cartilage becomes ossified, it affords by boiling not 

 chondrine but gelatine. 



As chondrine exists in cartilage, so gelatine is contained in 

 the bones, tendons, ligaments, the cellular or filamentous tissue, 

 membranes in general, and the skin. It has been affirmed, on 

 grounds that cannot easily be refuted, that gelatine has no 

 nutritive properties in short, that the use of it as a dietetic 

 substance is rather injurious. It appears that within the living 

 body it cannot be transformed into fibrine, albumen, or caseine, 

 and it is certain that animals fed exclusively on gelatine die 

 with symptoms of starvation. 



Grystallisdble Azotised Proximate Principles. 



Urea, Creatine and Creatinine, Uric Acid, Hippuric Acid. 

 Urea, creatine, and creatinine are crystallisable principles de- 

 rived from the disintegration of the muscular tissue destined to 

 be rejected from the living system as excrementitious. 



Urea is the chief peculiar constituent of the urine. It is 

 made up of oxygen, hydrogen, carbon, and nitrogen, the last 

 being the predominant element. The constituents of urea are 

 the same as those of albumen, fibrine, and caseine, yet their 

 proportions are very different. In that albuminoid group the 

 proportion of nitrogen is only about 1 5 per cent, while in urea 



