Milk. 155 



milk dried in thin layers at low temperatures leaves a 

 residue from which ether readily dissolves the fat, have 

 thrown the gravest doubt on this hypothesis. One recent 

 French writer, indeed, M. Bechamp, has endeavoured to 

 show that the milk globules are true physiological indivi- 

 duals, like blood corpuscles. By appropriate treatment he 

 has succeeded in separating them by nitration from the 

 rest of the milk. He states that when thus isolated and 

 dried they dissolve in ether, leaving about 1*3 per cent, of 

 a residue insoluble in ether, which he asserts is not casein, 

 but of the nature of a cell- wall. These views of the French 

 savant are, I think, opposed to the general current of 

 modern opinion on this matter, and his facts can probably 

 be explained without accepting his hyj)0 thesis. It seems 

 most likety that each globule of fat is surrounded by a thin 

 pellicle oi fluid casein. It is a fact well known to chemists, 

 that when a complex organic fluid is shaken with ether or 

 chloroform for the purpose of separating some constituent 

 soluble in these liquids, it is not uncommon for each globule 

 of ether or chloroform to become encased in just such a 

 liquid pellicle, which most obstinately resists our efforts 

 to break it up and bring about the union of the globules. 

 Milk itself very easily causes this condition of things when 

 shaken with ether. I have had, to my great annoyance, 

 frequent experience of this phenomenon, and have had 

 samples of this emulsion which remained intact for weeks 

 and even months, the ether refusing to separate as I wished 

 it to do. 



As to the chemical composition of butter fat a few words 

 will suffice. Fats are combination of certain organic acids 

 — " fatty acids " as they are called — with glycerine. Besides 

 stearic, palmitic and oleic acids, which are present in most 

 animal fats, butter is peculiar in containing more than 

 6 per cent, of butyric acid, which differs from those just 

 named by being soluble in water and volatile. This fact is 

 of great importance in enabling us to detect adulteration 

 of butter by admixture with foreign oils and lats. 



The quantity of fat in healthy cow's milk varies from 

 2-5 per cent, to 5 • 5 per cent., the average being a little 



