CHANGE OF CASEINE. 51 



served where no actually living surface is present : thus pure 

 charcoal saturated with strong vinegar, under very free expo- 

 sure to air, has the effect of changing dilute alcohol into a 

 large quantity of diluted vinegar the presence of the vinegar, 

 as it would seem, determining the conversion of the alcohol 

 into the same compound. Chemists, it is true, are not agreed 

 in the views taken of changes of this kind. But in the mean 

 time it is satisfactory to find that parallel cases in point of 

 fact can be brought together from different sources. What 

 is undeniable here that is, in the case of the first digestion 

 in the colt is, that in the body of the colt at birth there is 

 no casein e ; that nothing of the nature of a plastic substance, 

 except caseine, is contained in the mare's milk ; and, in parti- 

 cular, that there is no albumen or fibrine present ; that never- 

 theless albumen and fibrine, being the substances out of which 

 the chief organs and parts of the colt are built up, are both 

 present in abundance at the moment of birth, and go on 

 growing in quantity, while no plastic substance but caseine 

 is supplied prior to the time of weaning ; thus that this is not 

 improbably one of the cases in which the presence of a prox- 

 imate principle has a share in determining the conversion of 

 another proximate principle into itself. 



As already noticed, caseine contains very nearly the same 

 proportions of carbon, hydrogen, nitrogen, and oxygen, which 

 exist in albumen and fibrine. It contains also, like these two 

 principles, sulphur. It does not show phosphorus in its 

 composition. There are phosphates of potash, soda, lime, and 

 magnesia in mare's milk as in other kinds of milk ; and 

 from this source the phosphorus requisite for the conver- 

 sion of caseine into albumen or fibrine doubtless is derived. 

 For this purpose, however, the deoxidation of the phosphoric 

 acid in some of these phosphates is required. But deoxi- 

 dation is not a frequent mode of chemical action in the living 



