406 THE PHYSIOLOGY OF REPRODUCTION 



a supply of calcium for the foetus is not known (Fig. 95). 

 There is at present no evidence that they are " protein 

 crystals," a name sometimes applied to them. 



The uterine milk has thus the following constituents the 

 secretion of the superficial and glandular epithelium, perhaps 

 mingled with lymph transuded from the oedematous mucosa ; 

 leucocytes containing haemoglobin derivatives, fat globules, and 

 " Stabchen " ; glycogen ; tracts of glandular epithelium set free 

 by a process of " cellular secretion " ; red blood corpuscles and 

 their derivatives ; connective-tissue elements ; salts, &c., which 

 are in solution and not recognisable by ordinary histological 

 methods. 



While lying free in the uterine cavity, the uterine milk under- 

 goes changes which consist largely in a disintegration of its 

 cellular elements. The leucocytes degenerate and their cyto- 

 plasm, with the pigment granules, fat globules, and " Stabchen," 

 is set free. The tracts of glandular epithelium are also trans- 

 formed into a mass of debris, and their contents he free in the 

 embryotrophe. The red blood corpuscles may be ingested 

 almost unaltered by the trophoblast, or they may first be laked, 

 and the haemoglobin may be absorbed as such, or undergo 

 changes before absorption. According to Jenkinson, haemo- 

 globin is broken up into an iron-containing and an iron-free part. 

 The former is carried away by the foetal blood-vessels and 

 stored in large quantities, principally in the foetal liver, as a re- 

 serve for use during lactation. The iron-free part is deposited 

 in the cells as a pigment, occurring in such amount as to give, 

 especially in the later stages of pregnancy, a deep brown colour 

 to the foetal cotyledons. It collects at the apices of the villi, 

 and its presence suggests that the cotyledons are actively en- 

 gaged in excretion (Assheton). The histological changes in the 

 red blood corpuscles absorbed by the trophoblast have been 

 described by Jenkinson. They are engulfed by amoeboid pro- 

 cesses of the cells, and gradually become paler in colour and 

 irregular in outline ; often they clump together. Gradually 

 yellowish-brown granules are deposited on the surface of the 

 included cells, and this process continues till the whole is con- 

 verted into a dark brown mass. Bonnet called the granules 

 haematoidin crystals, but Jenkinson was unable to demonstrate 



