22 Physiology of Lactation and Characteristics of Milk in General. 



The milk formation occurs between the milking periods and 

 during the milkiiigs ; therefore of these two periods, the first lasts 

 for many hours, the second with more intensive production is com- 

 pleted in a few minutes. The first phase is the work of continued 

 activity of the gland, the second is brought on under the stimula- 

 tion of the sucking, or milking, on the secretory nerves, and as a 

 result of the increased blood supply (stimulation of the vasodila- 

 tors). The capacity of all the milk ducts of the udder represents 

 less than half of the quantity of milk obtained in one milking. 



According to Fleischmann the volume of the entire udder of a 

 cow with the teats is 6700 c. c. Of this 3000 c. c. is represented 

 by the cavities ; the secretion obtained in one milking may never- 

 theless amount to 7000 c. c. 



Niiesch substantiates Fleischmann 's statements by an experi- 

 ment; a cow gave daily before slaughter 10 liters of milk of 

 which 5 . 5 liters was the amount of the morning milking. 



After slaughter before milking in the morning 2.7 liters of 

 milk could be proven in the udder (catheterization and calculation 

 of the amount remaining in the udder), which proves secretion 

 during the process of milking. 



The two phases may be considered as though the glandular 

 cells which tire after the milking gradually recover (increased 

 blood supply) and recommence their secretions. The collecting 

 secretion will increase until a certain relative pressure between 

 the collective quantity of secretion and the tissue with the blood 

 vessels is established, when the secretion is retarded or ceases until 

 renewed stimulation of the glands by milking, emptying, massage, 

 (electric irritation), or stimulation of the central nervous system 

 from milk accumulations causes the milk to fill the cavities of the 

 udder again. 



If the usual milking time is omitted a flow of milk may result, 

 that is the pressure under which the secretion is held finally over- 

 powers the resistance of the sphincter muscles at the opening of 

 the teats (directly or by reflex), whereupon formation of milk 

 again takes place. 



Nervous influences on the secretion are exerted by the sper- 

 maticus externus and by the sympathicus. 



Experiments which were conducted for the study of the ener- 

 vating influences on the secretion produced contradictory results. 



Rohrig severed the ramus inferior of the nervns spermaticus 

 externus (vessel branch), and observed an acceleration of the 

 secretion, while the severing of the glandular branch (part of the 

 median branch) resulted in inhibition. Eckhard failed to observe 

 any influence on the quantity of milk after the severing of the ner- 

 vus spermaticus extermis. Heidenheim and Partsch demonstrated 

 an increase of the quantity of milk from the cutting of the nervus 

 spermaticus externus, but only when strychnine or curare had been 

 administered at the same time (test by Sinety on guinea pigs). 



