22 ORGANIC CONSTITUENTS. 



casein left only O'S'^. The ash contains phosphoric^ carbonic, 

 hydrochloric, and sulphuric acids, in combination with lime, 

 and traces of magnesia and iron. 



Diagnosis of casern. Casein may be distinguished from albu- 

 men by its not coagulating at 167°, and by the skin which 

 forms on its surface during evaporation. It is precipitated by 

 all dilute acids, and redissolves in an excess of the test. It 

 is thrown down from its acid solutions by ferrocyanide and 

 ferridcyanide of potassium. Casein of woman's milk is less 

 perfectly thrown down by dilute sulphuric, lactic, and hydi'o- 

 chloric acids, than the casein of cow's milk. 



Simon has obtained a modified form of casein from the crys- 

 talline lens,i from tubercle, pus, and saliva. 



It may be recognized as casein by the diagnosis which has 

 been given, but it differs from human casein in its thorough 

 precipitation by all acids ; and from the casein of human and 

 cow's milk byits greater solubilityin hot alcoholof 0"915 — 0-925. 



The globulin of Berzelius, which together with Immatin forms 

 the blood- corpuscles, is considered by Simon as a peculiar form 

 of casein. Very little is known regarding it, further than that 

 it is a protein-compound. Mulder^ represents it by the formula 

 15 Pr + S. 



It must not be confounded with Lecanu's globulin, which 

 is merely impure lii3ematin mingled with some albumen. 



Pepsin, Ptyalin, Chondrin, Glutin, Pyin. 



5. Pepsin. This name (from Tmraig, digestion) was given by 

 Sclnvann, to a siibstance which constitutes the most essential 

 portion of the gastric juice. The following directions for the 

 preparation of pepsin are taken from Vogel's essay on the sub- 

 ject ; they correspond in nearly every respect, with the method 

 which was given by Wasmann, who has the credit of first obtain- 

 ing it in an isolated state. The glandular membrane of the 

 fresh stomach of the hog, is separated, and after being cut into 

 small pieces, is treated with cold distilled water; after twenty- 

 four hours' immersion, the water is poured off, and a fresh quan- 

 tity added. This operation is repeated for several days, until 



' See Appendix I, Note 10. » lb. Note 11. 



