110 CHEMICAL COMPOSITION OF ANIMAL TISSUES. 



171. The ultimate composition of the Albumen of the blood may be 

 stated as follows : 



Carbon, - 548 



Hydrogen, - 71 



^ Oxygen, - 212 



Nitrogen, - - 159 



Sulphur, - 7 



Phosphorus, - 3 



1000 



. It has been maintained by Mulder, that the sulphur and phosphorus 

 may be completely separated from the substance formed by the union 

 of the first four elements ; and to this substance, he gave the name of 

 Proteine, believing it to be the base of the whole series of albuminous 

 compounds, which are supposed to consist of proteine, united with sul- 

 phur and phosphorus in varying proportions. It does not appear, how- 

 ever, that proteine has ever been really obtained in an isolated form ; 

 and its existence must at present be considered as hypothetical. It 

 may be convenient, however, to use the phrase " proteine-compounds," 

 to designate the whole series of Animal and Vegetable substances, 

 which are capable of being converted into Albumen in the digestive 

 process : and in this sense alone will it be here employed. The atomic 

 constitution of Proteine is considered by Liebig to be represented by 

 the formula 



49 Carbon, 36 Hydrogen, 14 Oxygen, 6 Nitrogen. 



whilst by Mulder the following formula is adopted 



40 Carbon, 31 Hydrogen, 12 Oxygen, 5 Nitrogen. 



Both these formulae are sufficiently conformable to the relative propor- 

 tions of the components ; but it has not been yet determined which best 

 represents the combining equivalent of the substance. 



172. Nearly allied to Albumen is the substance termed Caseine, 

 which replaces it in milk ; and this is specially worthy of notice here, 

 because it is the sole form in which the young Mammal receives Pro- 

 teine into its body, during the period of lactation. Like Albumen, this 

 substance may exist in two forms, the soluble, and the insoluble or coa- 

 gulated ; and it further agrees with it, in requiring, as a condition of 

 its solubility, the presence of a free alkali, of which, however, a very 

 small quantity suffices for the purpose. It differs from Albumen, how- 

 ever, in this : that it does not coagulate by heat, and that it is precipi- 

 tated from its solution by Acetic acid. Caseine is further remarkable 

 for the facility with which its coagulation is effected by the contact of 

 certain animal membranes, as in the ordinary process of cheese-making. 

 This change is considered by some Chemists to be due, however, not to 

 any direct action of the membrane upon the caseine, but to its influence 

 in converting some of the milk-sugar into lactic acid, w T hich, separating 

 the alkali of the caseine, will occasion the precipitation of the latter 

 The only difference which can be detected between Albumen and Case- 

 ine, in regard to the proportions of their elements, consists in the ab- 

 sence of Phosphorus, arid the smaller proportion of Sulphur, in the 

 latter ; but this can scarcely be the cause of the foregoing differences in 



