344 OF DIGESTION AND NUTRITIVE ABSORPTION. 



Sulphur J 



Thus it appears that the azotized vegetable principles may be converted into 

 those organic compounds which have been ordinarily considered as peculiar 

 to animals, without any essential change in their chemical composition. 



458. When Albumen or Fibrin is dissolved in a moderately strong solution 

 of caustic potass, and is heated to about 120, the small portions of phosphorus 

 and sulphur it contains are separated in the form of phosphate of potass and 

 sulphuret of potassium ; and when this solution is saturated with acetic acid, 

 a gelatinous substance is precipitated, which is the same in aspect and consti- 

 tution, whether obtained from fibrin or albumen. To this the term Protein 

 has been given. After being washed, it is still gelatinous, of a grayish colour, 

 and semi-transparent ; when dried, it is yellowish, hard, easily pulverized, 

 tasteless, insoluble in water and alcohol ; and, like fibrin and albumen, it is 

 not fusible by heat without decomposition. The formula for Protein, accord- 

 ing to Mulder, is, 40 Carbon, 31 Hydrogen, 5 Nitrogen, 12 Oxygen.* It 

 may be obtained equally well from the globulin of blood, from the casein of 

 milk, and from vegetable albumen ; whence it is evident that these substances 

 are all to be regarded as modifications of a common principle. The nature of 

 these modifications may be partly understood from the fact that Protein unites, 

 according to strictly chemical principles, with many inorganic substances; 

 forming new compound acids when combining with acids ; and acting in some 

 degree as an acid, when brought into relation with bases, such as the oxides 

 of lead and silver, of which one atom combines with 10 of protein. Viewed 

 as chemical compounds, fibrin and albumen may be regarded as the products 

 of the union of protein with definite proportions of sulphur and phosphorus. 

 The following are their formulae, according to Mulder. 



Fibrin, and the albumen of eggs . 10 Pro. + 1 Sulph. -f | Phos. 

 Albumen of Serum ..... 10 Pro. + 2 Sulph. + Phos. 



459. From these facts, taken in combination with those already mentioned, 

 it seems scarcely possible to resist the conclusion that the process of Digestion 

 (strictly so called) is one of a purely Chemical nature. The conversion of the 

 azotized animal and vegetable substances into Albumen, can scarcely be viewed 

 in any other light ; for the change of form and of external characters is in no 

 instance so great as that which starch and gum undergo during their con- 

 version into sugar, which is well known to be of a strictly chemical nature. 

 The albumen thus formed is dissolved in the water that has been ingested, 

 and in the gastric secretion; and becomes one of the most important and 

 characteristic ingredients of chyle. According to Dr. Prout, the albumen 

 which is first formed in the stomach, differs from the principle elsewhere 

 known under that name, in its imperfect coagulation, when acted on either by 

 acids or heat. This is noticed, even when pure albumen has been introduced 

 into the stomach ; for it is first coagulated, and then dissolved, so as to present 

 the same characters with the albumen formed from other substances. In this 

 process it appears to enter into chemical combination with a large quantity of 



* Liebig takes rather a. different view of its composition, which is, however, equally 

 conformable with analytic results. His formula is, 48 Carbon, 36 Hydrogen, 6 Nitro- 

 gen, 14 Oxygen. 



