604 THE PHYSIOLOGY OF REPRODUCTION 



mammary secretion is formed by the union of glucose, the normal 

 .sugar of the organism, with galactose, which is supposed to be 

 derived directly by hydrolysis from certain polysaccharide substances 

 introduced in the food. It is pointed out further, that such 

 substances are present in plants which form the normal diet of 

 certain animals. It would appear, however, that there is no direct 

 evidence that lactose is actually formed in this way. Moreover, 

 this theory can scarcely be applied to carnivorous animals, as 

 Porcher 1 has pointed out. 



There is, therefore, no definite evidence that lactose is elaborated 

 in the mammary glands from any closely related carbohydrate 

 precursor carried thither from elsewhere in the body. It is more 

 likely, as Hammond has suggested, that milk-sugar is derived from a 

 glycoprotein precursor which, mixing with water and salts from 

 the blood, contributes to the secretory product. As evidence of this 

 contention he refers to a number of experimental observations by 

 different physiologists besides recording a series of experiments of 

 his own. The evidence is summarised in the next paragraphs. 



Lusk 2 states that after administering phloridzin (which removes 

 glucose from the blood by causing it to be excreted in the urine) 

 to a goat the results were a reduction in the milk yield but an 

 increase in the percentage of fat. Similarly Porcher, 3 experimenting 

 on cows and goats, obtained a reduction in the milk yield. Paton 

 and Cathcart, 4 by injecting phloridzin, likewise produced a decrease 

 in the secretion together with a diminution in the lactose, nitrogen, 

 and ash. When the milk secretion was most reduced the sugar 

 excreted in the urine was greatest. Rose 5 found that the milk 

 secreted varied inversely with the phytin in the food, and that 

 when the latter was increased the percentage of fat in the milk 

 increased. 



Hammond & himself found that as a result of injecting pituitary 

 extract, which acts as a powerful immediate galactogogue (see below, 

 p. 621), the milk was normal in composition except for an increase 

 in the fat. (The daily yield was only slightly increased ; thus if the 

 goat was injected in the morning the milk secreted at that time 



1 Porcher, " Sur la Physiologic de la Mamelle," Jour, de Med. Vet. de VEcole 

 de Lyon, 30th September 1905. 



- Lusk, "Ueber Phloridzin-Diabetes," Zeitsch. f. Biol. (Festschr. B. Voit), 

 1901. 



3 Porcher, "L'Origine du Lactose," Arch. Internat. de Phys., vol. viii., 1909. 



4 Paton and Cathcart, "On the Mode of Production of Lactose in the 

 Mammary Gland," Jour, of P/iysiol., vol. xlii., 1911. 



5 Rose, " A Study of the Metabolism Effects of Certain Phosphorous Com- 

 pounds," New York State, State Tech. Bull., 1912. 



6 Hammond, "The Effect of Pituitary Extract on the Secretion of Milk," 

 Quart. Jour. Exp. PhysioL, vol. vi., 1913. Hammond and Hawk, " Studies in 

 Milk Secretion," Jour. Agric. Science, vol. viii., 1917. 



