THE PROTEIN SUBSTANCES. 37 



alkalies at the ordinary temperature, and only slowly at the boiling 

 temperature. It is very slowly attacked by cold concentrated sul- 

 phuric acid, and it is relatively easily dissolved on warming with 

 strong nitric acid. It gives MILLON'S reaction. 



On account of its great resistance to chemical reagents, elastin 

 may be prepared (best from the ligameiitum nuchae) in the fol- 

 lowing way : First boil with water, then with \% caustic potash, 

 then again with water, and lastly with acetic acid. The residue 

 is treated with cold 5$ hydrochloric acid for twenty-four hours, 

 carefully washed with water, boiled again with water, and then 

 treated with alcohol and ether. 



Collagen, or glue-forming substance, occurs very extensively in 

 the animal kingdom, especially in the vertebrates, seldom in the 

 invertebrates. Collagen is the chief constituent of the fibres of 

 the connective tissue and (as ossein) of the organic substances of 

 the bony structure. It also occurs in the cartilaginous tissues as 

 chief constituent, but it is here mixed with another substance 

 which was formerly called chondrigen. Collagen from different 

 tissues has not quite the same composition, and probably there are 

 several varieties of collagen. 



By continuously boiling with water (more easily in the presence 

 of a little acid) collagen is converted into gelatine. HOFMEISTER 

 found that gelatine, on being heated to 130 C., is transformed into 

 collagen; and this last may be considered as the anhydride of gela- 

 tine. Collagen and gelatine have the following composition : 



C H N S+0 



Collagen 50.75 6.47 17.86 24.92 (HOFMEISTER.) 



Gelatine (from hartshorn) . 49.31 6.55 18.37 25.77 (MULDER.) 



Gelatine (from bones) 50.00 6.50 17.50 26.00 (FREMY.) 



The gelatine contains about 0.6$ sulphur, which probably be- 

 longs to the gelatine and hardly exists there as an impurity from 

 the albumin. 



The investigations in regard to the decomposition products of 

 collagen have been made on gelatine. Gelatine yields, under simi- 

 lar conditions as albuminous bodies, amido-acids, but no tyrosin. 

 It yields a large amount of glycocoll, to which, on this account, the 

 name of glue-sugar has been given. On putrefaction gelatine gives 



