INTERMEDIATE PRODUCTS. 65 



4. Elastin is obtained from yellow elastic tissue by boiling with 

 caustic alkalies. It is little affected by boiling water, strong acetic 

 acid, or weak alkalies, but dissolves in concentrated sulphuric 

 acid. It is precipitated by tannin, and yields leuciu when boiled 

 with sulphuric acid. 



5. Keratin exists in the epidermic appendages (hair, horn, nails, 

 etc.). It is like the albuminous bodies in containing a considera- 

 ble quantity of sulphur, but differs from them and the other albu- 

 minoids in general properties. It is soluble in alkalies, swells in 

 strong acetic acid, gives the xanthoproteic reaction, and is ex- 

 tremely insoluble in the digestive juices. 



Group IV. PRODUCTS OF TISSUE CHANGE. 

 Intermediate or bye products. 



These are, no doubt, protoplasmic manufactures destined for 

 some useful purpose, but they do not long exist in their original 

 form, being often broken up into other compounds they are re- 

 absorbed, or pass away with the faeces. These bodies are found 

 in the various secretions. Most of them, however, can be better 

 described with the function of the gland which forms the secre- 

 tion iu which they occur. 



Attention must here be drawn however to certain complex 

 bodies existing in the bile. Some complex nitrogenous substances 

 and the mouatomic alcohol, cholesterin, will also be now men- 

 tioned. But the reader must remember that chemically they are 

 not connected with the other bodies the description of which im- 

 mediately follows theirs, namely, the effete products. 



Bile Salts. Two acids exist in the bile united with soda to form 

 soluble soap-like salts. They may be recognized by the purple- 

 violet color produced by cane-sugar and sulphuric acid at a tem- 

 perature of about 70 C. (Pettenkofer's reaction). 



Taurocholie Acid, C 26 H 45 NSO 7 , is most plentiful in the bile of 

 carnivora and man, where it occurs combined with soda. It is 

 decomposd by prolonged boiling with water into taurin and cholic 

 acid, thus : 



Taurocholie acid. Taurin. Cholic acid. 



C 26 H 45 NS0 7 + H 2 = C 3 H t NS0 3 + C 24 H 40 O 5 - 

 6 



