CHAPTEB II. 



PHYSIOLOGY OF LACTATION AND CHARACTERISTICS OF 

 MILK IN GENERAL. 



As already mentioned the udder secretes only in certain 

 lactation periods between births. The lactation lasts under nat- 

 ural conditions in healthy animals as long as the young needs 

 the glandular secretion for its nourishment, and stimulates the 

 lactation by the irritation of the intermittent suckling. Shortly 

 before parturition, or at the time of parturition, the glandular 

 tissue terminates its increase in development, and the milk secre- 

 tion starts and becomes actively established. 



The causes of the increased cell production during pregnancy, 

 and for the secretion after this time, are variously explained. 

 Nervous irritation from the genitals to the milk glands may by 

 means of reflex action stimulate the glands into activity. 



That such reflexes on the genitals may originate from the 

 milk gland is proven (Pfaundler). Reflex actions in the opposite 

 way, however, have not been proved (Halbau). 



It has been impossible either experimentally (extirpation of 

 the lumbar cord) or by accident (fracture of the spine), to pro- 

 duce a complete " nervous isolation," since as emphasized by 

 Pfaundler, there are still remaining the nervous connections 

 through the vasomotors. However, the re-section of nerves, oper- 

 ations on the spinal cord, transplantation experiments, etc., by 

 Eckhardt, Rohrig, Sinety, Busch, Mirnow, Piaster, Ribbert, Golts 

 and Ewald would suggest that besides the nervous influences, 

 which undoubtedly exist, there must be some other agent which 

 stimulates continuous growth during pregnancy, terminates the 

 same with the end of parturition, and inaugurates the secretion. 



Hematogenic influences may be readily accepted, as they may 

 be led to exert their action either by the quantity or by the quality 

 of the blood. 



After parturition the body and the milk gland have at their 

 command great quantities of blood which was previously utilized 

 by the gravid uterus. The plethora which appears at this time 

 may be held responsible for the inauguration of the secretion, 

 after the udder has been rendered ready for action by the increase 



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