CONSTITUENTS OF HUMAN MILK. 321 



Sugar. Carter and the author found that the sugar crystal- 

 lised in rhomboid plates (not the wedge-shaped crystals of milk- 

 sugar), and had a specific rotatory power of [ct] D = 48-7. 



The sugar was estimated by difference in the milk, as it was 

 found that polarisation and estimation by Fehling's solution 

 did not give satisfactory results. It was found that the gravi- 

 metric results were from 0-56 to 0-98 per cent, below the difference, 

 and averaged 0-71 per cent, below, while the polarimetric results 

 were from 0-85 to 2-22 per cent, below the difference, and 

 averaged 1-30 per cent, below. 



The refractive index appears to decrease progressively as 

 lactation proceeds. 



It was noted that by precipitating the sugar crystallised from 

 water with dilute alcohol an amorphous substance separated, 

 soluble in water. The [a] D of the organic solids of the mother 

 liquor from which the sugar was crystallised was 26-8. These 

 facts seem to indicate that more than one sugar was present. 



As the author has since found that acid mercuric nitrate does 

 not precipitate all the Ixvo -rotatory substances, there is some 

 doubt as to whether the sugar of human milk examined by 

 Carter and Richmond is not lactose not in a state of purity, 



Proteins. The proteins differ from those of cow's milk by not 

 giving a curd with rennet, and by giving a much finer precipi- 

 tate with acids. By the addition of calcium phosphate they 

 can be made to approach much more nearly in behaviour to 

 those of cow's milk. The proteins of human milk are not 

 precipitated by copper sulphate from a solution neutral to 

 phenol-phthalein, but require a further addition of alkali ; the 

 precipitate thus obtained yields a black ash, while the proteins 

 of cow's milk precipitated from a neutral solution leave a green 

 ash. 



The casein of human milk, though closely related, differs 

 from that of cow's milk ; it is not curdled by rennet, does not 

 exist in combination with calcium phosphate, and is thrown 

 down by acids in a finely divided state, though Engel finds that 

 if 10 grammes of human milk are mixed with 50 c.c. of water 



N 

 and 6 to ^ c.c. of -^ acetic acid, kept at C. for two or three 



hours, and then warmed to 40 C. with frequent stirring, the 

 casein separates easily. Dolgrel advises the addition of salts 

 to make the casein flake. Kolbrak considers human casein less 

 acid, and finds that on continued precipitation with acid and 

 solution in alkali it becomes more and more like cow's casein. 

 Lehmann and Hempel find 1-09 per cent, of sulphur and 3-2 

 per cent, of ash in the casein of human milk separated by a 

 porous plate as against 0-72 and 6*47 respectively for cow's 



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