856 THE PHYSIOLOGY OF REPRODUCTION. 



produced abundantly during the period of lactation under the in- 

 fluence of the act of milking. If during this period a new con- 

 ception occurs the milk secretion is altered in composition and 

 finally ceases. On the other hand, if the act of nursing is aban- 

 doned permanently the glands after a preliminary stage of turgid- 

 ity undergo retrogressive changes that result in the cessation of 

 secretory activity. The colostrum secretion that occurs during 

 pregnancy and for a day or two after birth differs from milk in 

 its composition and histological structure. It is a thin, yellowish 

 liquid containing a larger percentage of albumin and globulin 

 and a smaller percentage of milk-sugar and fat than normal milk. 

 Under the microscope it shows, in addition to some fat droplets, 

 certain large elements, the colostrum corpuscles. These con- 

 sist of spherical cells filled with fat droplets, and are most probably 

 leucocytes filled with fat which they have ingested. Colostrum 

 corpuscles may occur in milk whenever the secretion of the gland 

 is interfered with, and their presence may be taken as an indi- 

 cation of an incomplete secretion. 



The Connection Between the Uterus and the Mammary 

 Gland. The physiological connection between the uterus and 

 the mammary gland is shown by the facts mentioned in the pre- 

 ceding paragraph. That the ovary also shares in this influence 

 either directly or through its effect on the uterus is shown by 

 the fact that after complete ovariotomy the mammary gland under- 

 goes atrophy. This undoubted influence of one organ upon the 

 other might be exerted either through the central nervous system 

 or by way of the circulation. There are indications that the 

 secretion of the mammary glands is under the control, to some 

 extent at least, of the central nervous system. For instance, in 

 women during the period of lactation cases have been recorded 

 in which the secretion was altered or perhaps entirely suppressed 

 by strong emotions, by an epileptic attack, etc. This indication 

 has not received satisfactory confirmation from the side of ex- 

 perimental physiology. Eckhard found that section of the main 

 nerve-trunk supplying the gland in goats, the external spermatic, 

 caused no difference in the quantity or quality of the secretion. 

 Rohrig obtained more positive results, inasmuch as he found that 

 some of the branches of the external spermatic supply vasomotor 

 fibers to the blood-vessels of the gland and influence the secretion 

 of milk by controlling the local blood-flow in the gland. Section 

 of the inferior branch of this nerve, for example, gave increased 

 secretion, while stimulation caused diminished secretion, as in the 

 case of the vasoconstrictor fibers to the kidney. These results 

 have not been confirmed by others in fact, they have been sub- 



