288 
Milk. 
Composition of Casein. 
Carton 53-57 
Hydrogen 7-14: 
Nitrogen 15-41 
Oxys;cn 22-03 
Siilphur 1-11 
Phosphorus -74 
100-00 
Pure casein of milk has almost precisely the same composition 
as vegetable casein, or legumin, and possesses the same physical 
and chemical properties. 
Vegetable casein, I may observe in passing, is far more abun- 
dant in plants than albumen. Since fibrin or muscular fibre, 
Avhich contains phosphorus, can as readily be produced from 
casein or legumin, as from albumen in Avhich phosphorus is a 
recognised constituent, it may be reasonably expected that casein 
and legumin should also contain this element. 
I find, indeed, that all the members of the group of albuminous 
or flesh-forming matters contain phosphorus, as well as sulphur ; 
Avhich indicates that there is nothing wanting in the composition of 
any of them which might render any one less useful than another 
as a flesh-producing material. It is difficult to obtain casein 
entirely free from mineral matters. Phosphate of lime especially 
clings to casein with great pertinacity, — a circumstance which has 
prevented scientific chemists from recognizing the existence of 
organic phosphorus in casein. By organic phosphorus we 
mean phosphorus chemically united with carbon, nitrogen, and 
the other ultimate organic constituents of casein. 
In this intimate organic combination the usual properties of 
phosphorus remain entirely concealed, and the most delicate 
tests fail to trace its existence unless the casein be completely de- 
composed by chemical means, or until it has been subjected to 
putrefaction. When the latter sets in, phosphorctted hydrogen 
appears amongst the gaseous products formed. v 
In the preceding analysis the ash, amounting to only "317 per 
cent., has been deducted previous to calculating the composition 
in 100 jiarts. About one-third of the ash, or in exact numbers 
"11 percent., was phosphate of lime. It will be seen that the 
amount of phosphorus which I discovered in casein is greater 
than the total amount of ash, showing clearly that phosphorus 
occurs in casein in combination with the organic elements, car- 
bon, hydrogen, nitrogen, and oxygen, and not exclusively in an 
oxydized state as phosphoric acid. It is true, phosphate of lime 
cannot be completely removed from casein, but by careful puri- 
fication its amount may be reduced to a minimum. Moreover, 
