358 A TEXTBOOK OF PHYSIOLOGY 



ment: A male and a female mouse were rendered immune to a poison 

 (abrin). Each was then mated to a non-immune companion. It was 

 found that the offspring of the immune male and non-immune female 

 possessed no immunity against the poison. On the other hand, the 

 offspring of the non-immune male and of the immune female possessed 

 such an immunity, which gradually increased after birth, and was 

 therefore not derived solely from the placenta. The offspring were 

 then changed. The immune female suckled the non-immune young, 

 the non-immune female suckled the immune young. It was found 

 that the former soon acquired an immunity, the latter quickly lost 

 their immunity to the poison. 



Of the infant mortality under one year, and particularly under 

 eight months, the great proportion of deaths in some cities as large 

 as 170 per 1,000, over 300 in Russia is among artificially fed babies. 

 It must be borne in mind that such deaths are largely among the 

 very poor, and the artificial food in such cases is often inadequate, 

 and certainly not kept sterile and clean. The case against artificial 

 feeding is largely a case against careless or ignorant artificial feeding. 

 With a properly prepared clean food, such as the child can digest, 

 and containing the " building stones " suitable for its adequate 

 growth, there is every reason to believe that the child develops, in 

 most cases, into just as healthy a babe as does the breast-fed infant. 

 The introduction of dried milk has proved of the greatest import- 

 ance in lessening infant mortality. 



The mother should be urged to suckle the child during the first 

 months as much for her own sake as for the child's. The act of suckling 

 exerts a tonic effect upon the uterus. It assists in stopping haemor- 

 rhage from the placental site, and helps to secure the proper involution 

 of the uterus. 



The Secretion of Milk The Mechanism of Secretion. During 

 pregnancy, preparation is made for the feeding of the young. The 

 mammary glands begin to increase in size the engorged veins testify 

 to the activity taking place ; there is great proliferation of the alveolar 

 cells and duct epithelium. This takes place under the influence of 

 a hormone produced by the corpus luteum of the mother, and possibly 

 by the foetus itself. Nervous connections of the gland are not essen- 

 tial. The gland may be transplanted in the pregnant animal, and will 

 continue to proliferate. After birth, the proliferated resting glands 

 enter into a state of great secretory activity, possibly owing to the 

 removal of an inhibitory influence from the foetus. The first secreted 

 fluid is known as " colostrum." This is secreted for the first few days, 

 and is then followed by the supply of the milk proper. The secretion 

 is under both nervous and chemical agencies. The sucking efforts of 

 the offspring are a great factor in producing a good supply of milk. 

 For this reason, the new-born child should be frequently put to the 

 breast, even though the supply of food be scanty. It has been shown 

 in animals that various chemical bodies, such as pituitary extract (see 

 p. 523), and extract of the involuting uterus, when injected, cause an 

 increased flow of milk. It is stated, also, that in woman the injection 



