350 COLLOIDS IN BIOLOGY AND MEDICINE 



elements in cows' milk (casein and fat) may be definitely recognized 

 in the dark field though only the fat globules can be recognized in 

 human milk. The submicrons are larger in asses' and cows' milk but 

 largest in ewes' milk. In boiled milk the submicrons are larger and 

 disappear more slowly under treatment with solvents (potash, gastric 

 juice) than in unboiled milk, which is an indication that unboiled milk 

 is more easily digestible than boiled milk. 



Human and cows' milk may be distinguished by their ascent or rise 

 in strips of filter paper and their diffusion on blotting paper. For 

 instance, according to A. KREIDL and LENK * in 150 minutes cows' 

 milk ascends only 2.5 cm., while human milk ascends 10.8 cm. 

 According to LENK* this is chiefly due to the viscosity which in 

 turn depends on the amount of albumin and casein contained. If 

 a drop or two of cows' milk is placed on blotting paper, three zones 

 (fat, casein and solution of crystalloids) are observed, whereas human 

 milk exhibits but two (fat and other ingredients). 



I refer to page 173 et seq. for the methods of examining milk and 

 dairy products. 



It is necessary for completeness to mention the formation of skin 

 on boiled milk. The phenomenon is obviously analogous to the 

 formation of solid skins on dyes and peptone solution (see p. 33 

 et seq.). 



Referring to the changed condition of the surface, it might well 

 be worth finding out whether the unavoidable shaking during 

 prolonged transportation damages milk. We learn from clinical 

 experience that raw milk is more easily digested than boiled milk. 

 [From the fact that boiled milk forms smaller curds, it offers a larger 

 surface and on this account may be more readily passed through the 

 pylorus. It may even remove acid from the stomach by adsorption. 

 Tr.] This has been attributed to the presence of enzymes, which 

 are destroyed on heating, though no one has ever been able to give 

 any proof of the action of these enzymes. The most recent results 

 of research indicate that considerable changes in condition are as- 

 sociated with boiling. 



O. GROSSER l found by ultrafiltration that the lime was attached 

 more firmly to the milk colloids in boiled milk than in unboiled 

 milk. The ultrafiltrates of boiled milk contained less lime than those 

 of unboiled milk. The nitrogen and phosphorus content were 

 diminished in human milk, by boiling, but in cows' milk it remains 

 approximately the same. For instance, GROSSER found the follow- 

 ing quantities of CaO in ultrafiltrates: 



1 According to a private communication (as yet unpublished). 



