344 MILK. 



so imperfectly investigated, that we can scarcely be said to know 

 anything in relation to this subject. Herberger found that the 

 milk of cows having the murrain, was richer in potash, and had a 

 colostrum-like appearance. The milk becomes more watery in 

 almost all morbid affections, and is then also especially poor in 

 butter. In febrile affections it is frequently very acid. 



Almost every experimentalist has adopted his own plan of 

 analysing the milk, but as scarcely any methods before Haidlen's 

 can lay claim to accuracy, it is unnecessary to give a critical notice 

 of them, and we will here simply draw attention to the difficulties 

 which appertain to the quantitative analysis of milk, more than to 

 that of many other animal fluids. These difficulties extend, how- 

 ever, to nearly all of its individual constituents, and mainly depend 

 upon the following conditions : While undergoing the process of 

 evaporation, the milk becomes covered by the well known casein- 

 membrane, which during rapid evaporation is often broken by 

 vesicles of steam, by which a portion of the fluid may spirt out 

 and be lost. It is extremely difficult to dry the milk completely 

 after it has once undergone evaporation, and indeed almost 

 impossible unless a very small quantity of this fluid has been 

 employed for the determination of the solid residue ; for the dry 

 casein, when penetrated by fat, forms a crust which is impermeable 

 to water, and even to vapour. The casein is not perfectly thrown 

 down from the solution by means of acetic acid (see vol. l,p. 383), 

 since some portion may be extracted by alcohol as well as by 

 water. When acetic acid is employed, the acid enters into com- 

 binations with alkalies, and augments the alcoholic extract in a 

 manner which it is not easy to control, or even to estimate. The 

 fat cannot be perfectly extracted from the simple residue of the 

 milk, however long the latter may have been submitted to the 

 action of ether. On evaporating sour milk, the sugar is in part 

 converted into grape-sugar, or into an uncrystallizable syrup- 

 like sugar. When milk is exposed to a warm temperature, the 

 so-called extractive matters are formed in considerable quan- 

 tity. It is more difficult to incinerate the residue of the milk than 

 that of many other fluids. We are not yet able to make even an 

 approximate determination of the investing membranes cf the 

 milk-globules. 



Dumas and Scherer suggest, as a method for determining the 

 casein with every possible accuracy, that the milk, after it has been 

 evaporated in a water-bath or in a vacuum with sulphuric acid 

 till it is nearly dry, should be treated with a little acetic acid, and 



