88 IMMEDIATE PRINCIPLES OF THE TISSUES. 



fibrine, mucosine, &c., in the solids or fluids containing these sub- 

 stances as immediate principles. But that it is mostly converted 

 into albumen is probable from the fact that in diseases, if very little 

 food (or none) is taken, it disappears in the blood, and subsequently 

 the albumen itself also diminishes. It was this in the fluid dis- 

 charged in cholera which Guterbock mistook for caseine, there being 

 also very little albumen in choleric discharges. (Robin and VerdeiL) 



3. Caseine. 



Caseine is found, in animals, in milk only, 1 constituting 2 to 4 

 per cent., increasing as lactation proceeds, and being more abundant 

 during an animal than a vegetable diet. Its properties generally 

 resemble those of albumen; but all acids (as well as alcohol) do 

 coagulate it, while heat does not. 



It holds even more phosphate of lime (5 or 6 per cent.) in solution 

 than albumen. The salts are merely mixed, and are partly precipi- 

 tated with it in coagulating. A considerable quantity of water 

 mixed with it is also set free by its coagulation. 



A peculiar property of caseine is its coagulation from the contact 

 of an animal membrane, as in the case of the curd (caseine) in 

 making cheese. Some suppose that the pepsine in the rennet (the 

 dried and salted digesting or fourth stomach of the calf), coagulates 

 the caseine by catalysis, since the rennet will produce this effect 

 after all traces of acidity (from the gastric fluid in it) have disap- 

 peared. Others maintain that the rennet converts the sugar of milk 

 into lactic acid, which uniting with the alkali holding the caseine 

 in solution, the latter is precipitated in the solid form. But caseine, 

 like albumen and fibrine, is naturally fluid (Robin and VerdeiT); and 

 Lehmann remarks that the true cause of its coagulation is still un- 

 known. The acids of the stomach will, however, also coagulate 

 caseine, and the caseine of human milk is not precipitated by rennet 

 without the assistance of acids. 



1 MM. Guillot and Leblanc, mistaking albuminose for it, have announced its 

 presence in solution in the blood of man, woman, and several of the lower ani- 

 mals, and state that it is most abundant in the blood of women just before delivery 

 and during lactation. Simon observes that it exists in the blood of lactating wo- 

 men if the secretion of milk is checked. Panum has also found a substance in 

 blood-serum which he calls serum-caseine. It is extremely probable that caseine 

 does exist in the blood of women during lactation, but its presence there cannot be 

 regarded as yet demonstrated. 



