18 Physiology of Lactation and Characteristics of Milk in General. 



riches her blood with the so-called "milk producing substances." 

 Pfaundler recommends the designation "offspring nutritive pro- 

 ducing substances." Since during pregnancy the continuously 

 developing placenta utilizes and consumes these substances for use 

 in the nourishment of the young, there remain for the milk gland 

 only slight remnants, just sufficient to result in the necessary stimu- 

 lation for the cellular increase in the gland. After parturition 

 when the activity of the placenta is completed, the milk gland takes 

 up the released nutritive substances for its own use (specific af- 

 finity of the substances to the cells of the milk gland), and is 

 stimulated to secretion by the quantity of the disposable material. 

 Schein's milk producing substances in the blood constitute the 

 initial material for the formation of specific components of the 

 milk, milk sugar, casein and milk fat. 



The material acquired by the mother, through placental con- 

 tact with the fetus, while aiding in the development of the latter 

 is also of benefit to the activity of the milk gland, whose product 

 adapts itself exactly to the requirements of the young, as far as 

 it concerns the material which the young uses for the growth of 

 its body. 



If conception again takes place the developing placenta of 

 the new fetus enters into competition with the lactating gland, and 

 draws from it milk producing substances for its own use, whereby 

 the secretion of the milk gland becomes reduced or ended. 



Influences exerted on the milk gland by oestrum or puberty, 

 and also the impulse of pregnancy, have not yet been sufficiently 

 explained through this theory. Pfaundler enlarges upon and ex- 

 plains these phenomena by stating that the withdrawal of certain 

 nutritive substances, through the germinal gland, embryo and 

 ovum, and not the appearance of milk producing substances alone, 

 periodically disturb the equilibrum of physiologically acting sub- 

 stances in the blood, and thereby the antagonizers of those sub- 

 stances (the stimolines, harmones of other authors), are enabled 

 to find specific receptors (affinities) in other organs of the genital 

 apparatus. 



After birth, continuing intermittent stimulation may retain or 

 increase the lactation of the milk glands for a longer or shorter 

 time. Stasis of the milk diminishes and retards the secretion. 



Rievel opposes Schein's view, since in his opinion it does not 

 explain how udders of animals in which neither pregnancy nor 

 birth has preceded, could start secretion (lactation of milk glands 

 of the newly born or virgins, occasionally even of male animals). 

 According to the author's view these facts would not oppose the 

 theory of nutritive substances. Schein, himself, aims to bring 

 these observations into harmony with his views, and asserts that 

 the newly born may give a secretion from their milk glands, when 

 towards the end of pregnancy the activity of the placenta is dis- 

 turbed, and as a result small quantities of the "milk producing 



