ix THE SKIN AND CUTANEOUS GLANDS 513 



the genital organs and the mammae, due in all probability to a 

 reflex nervous influence between the two organs. 



Nothing but a reflex nervous excitation can explain the fact 

 that periodic suckling or milking is necessary to keep up the 

 lacteal secretion. In order to stop it, either in the first days after 

 parturition or at any subsequent period of suckling, it is only 

 necessary to interrupt the periodic evacuation of the gland. 



When the gland spaces have been emptied they gradually fill 

 up again, rapidly at first, and afterwards more slowly, until at 

 a certain degree of tension the secretion ceases entirely, and the 

 milk is gradually reabsorbed. It is certain that sucking at the pap 

 or milking the udder does not merely empty the gland of the 

 milk already secreted, but also reflexly promotes the further 

 secretion. According to Heidenhain, the glandular spaces of the 

 udder of a good milch cow have a capacity of about 3000 c.c., this 

 being the difference in volume before and after evacuation. A 

 Swiss cow is known to yield a quantity of milk far in excess of 

 3 litres at a single milking. It is therefore clear that the milking 

 not merely empties the udder, but also activates the secretion 

 of new milk. This is also proved by the fact that frequent 

 milking considerably increases the yield of milk in a cow, but it is 

 not advisable to trade upon this fact, since the animal's general 

 nutrition would deteriorate. 



Lehrnann (1887) injected a solution of indigo-carmine (sodium 

 sulphindigotate) into a milch goat, and at once began to milk her. 

 The first milk kept its colour, then it became slightly tinged, and 

 (after the lapse of an hour or an hour and a half) it became a 

 definite blue. This proves that the secretion is promoted by 

 milking. 



Another proof of nervous influence on the milk secretion is 

 seen in the fact that milking causes considerable alteration in the 

 composition of the secretion. While the glands are emptying the 

 fat content increases, and that of caseinogen Diminishes. Accord- 

 ing to Keiset the difference between the first and second milk is 

 greater in proportion with the interval between the two milkings. 

 This phenomenon seems to us inexplicable, unless it be admitted 

 that the mechanical stimulation of the teat exerts a reflex trophic 

 action on the secretory cells. 



Certain observations of Baglioni (1907) agree with the above. 

 In a nursing woman he saw that when the child was put to one 

 of the breasts and began to suck greedily (especially when the 

 breasts were very full), a copious gush of milk came spontaneously 

 from the other breast. Evidently this is a reflex, in which the 

 stimulation of one breast excites secretion in the opposite breast 

 also, either by increasing the secretory activity, or by producing 

 a contraction of the plain muscular fibres of the milk ducts, on 

 which the milk is ejected. That such a phenomenon really takes 



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