508 PHYSIOLOGY CHAP. 



circulating with the lymph in the gland, is seen from the fact that 

 bitches fed with an exclusively flesh diet excrete large quantities 

 of sugar in their milk (Ssubotin). It is therefore a mistake to 

 feed wet nurses on thick soups and farinaceous foods, with the 

 object of increasing the supply of milk. Protein substances should 

 be the basis of a rational diet for nursing women. 



Starting from the hypothesis that the lactose of the milk 

 originates in a process of conversion by the secretory gland-cells of 

 the dextrose of the blood, P. Bert (1884) excised the udder of a 

 goat, after which she became pregnant and gave birth. For three 

 days after parturition, the urine contained sugar, since it reduced 

 cupric oxide. To account for this transitory glycosuria he assumed 

 that after parturition glucose was normally formed more abundantly 

 than usual, and was converted into lactose in the mammary gland. 

 As the udder had been excised in the goat experimented on, the 

 puerperal hyperglycaemia gave rise to glycosuria. But it seems 

 to us far simpler to account, for the fact observed by Bert, by 

 referring the temporary glycosuria to injuries of parturition. In 

 any case it would be advisable to check the fact, by determining 

 what kind of sugar was present, and otherwise extending and 

 varying the experiment. We know from Hofmeister (1878) that 

 the urine of women and mammals in general often contains 

 lactose immediately before and after parturition, which is due 

 presumably to reabsorption of the lactose formed by the cells of 

 the mammary glands. 



Paul Bert's experiments were repeated by Porcher in 1905 

 with the same results. He further found that cows, goats, and 

 bitches into which glucose is injected in small doses subcutaneously, 

 or by the peritoneum or mammary gland, are capable of excret- 

 ing it during lactation as lactose in the urine, which lends support 

 to the view that the mammary glands really effect a conversion of 

 glucose into lactose. Piantoni (1908) came to the same conclusion, 

 on studying the effect on the lacteal secretion of a milch goat of 

 the subcutaneous injection of various sugars (lactose, galactose, 

 glucose-, saccharose, raffinose, and dextrin). 



According to C. Foa and Andreoni (1908) there is no percentage 

 difference in the content of the substances (glucose, glucoproteins, 

 glycogen) from which lactose originates, in the blood of women 

 who are suckling and not suckling. On comparing the content of 

 these substances in the carotid blood with that of the blood that 

 has traversed the gland, he finds a marked diminution in the 

 latter of free glucose and of that which is combined with the 

 proteins, while the glycogen is not diminished. 



IX. The exact cytological and chemical mechanism by which 

 the milk is secreted from the epithelial cells which line the alveoli 

 of the mammary gland, is still a matter of dispute. 



It was formerly held that the milk is discharged, on analogy 



