FUNCTIONS OF THE MAMMARY GLANDS. 289 



of milk/' says Foster, "but it becomes milk only through the 

 activity of the cell, and that activity consists largely in a 

 metabolic manufacture by the cell, and in the cell, of the 

 common things brought by the blood into the special things 

 present in the milk. Experimental results tell the same tale." 

 Another feature which it places on a solid footing when asso- 

 ciated with Professor Foster's research, and one which we wish 

 particularly to emphasize, is the identity of the liquid which 

 holds the various constituents of milk in solution, viz.: blood- 

 plasma. This is also suggested by a statement of M. Duval's, 

 who, referring to the formation of cream, says: "The trans- 

 parent portion that remains at the bottom of the vessel repre- 

 sents the plasma of the milk: that is to say, the milk without 

 globules. We employ the word 'plasma' here to establish a 

 parallelism between the analysis of milk and that of the blood. 

 Skimmed milk corresponds to the liquor of the blood." 



In the chapter on "Immunity" the true identity of blood- 

 plasma, owing to its inherent oxidizing substance, its alexins, 

 etc., as a prophylactic, and its role in this connection, will be 

 further studied. But, bearing directly upon the question in 

 point, i.e., the functional mechanism, the presence of plasma 

 in the milk forcibly indicates that an important vasoconstrictor 

 system must exist in the mammary gland. In fact, that so 

 careful an investigator as Laffont should have observed vaso- 

 dilation further emphasizes this, and tends to indicate that a 

 process similar to that described by us in our analysis of sub- 

 maxillary functions must prevail, i.e., indirect vasodilation, 

 a fact sustained by the counter-experiments of an equally com- 

 petent physiologist, de Sinety, who was unable to find vaso- 

 dilators per se. Laffont reached his deduction that vasodilation 

 occurred by measuring the blood-pressure in the mammary 

 artery of a bitch, during lactation, after severing the mammary 

 nerve and stimulating the peripheral segment of the latter. 

 Congestion of the gland and increase of milk-flow followed, 

 but after cessation of the artificial stimulation the flow, though 

 not arrested, was greatly reduced. This led Laffont to con- 

 clude inferentially that the mammary gland possessed typical 

 vasodilators similar to those thought to exist in the submax- 

 illary gland. We have shown that the phenomena upon which 



