438 THE PHYSIOLOGY OF REPRODUCTION 



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, etc., 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 cytoplasm, with the 

 pigment granules, fat globules, and " Stabchen," is set free. The 

 tracts of glandular epithelium are also transformed into a mass of 

 de'bris, and their contents lie 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, 

 haemoglobin is broken up into an iron-containing and 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 reserve 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 fostal cotyledons. 

 It collects at the apices of the villi, and its presence suggests that 

 the cotyledons are actively engaged in excretion (Assheton). The 

 histological changes in the red blood corpuscles absorbed by the 

 trophoblast have been described by Jenkinson. They are engulfed 

 by amceboid processes 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 

 converted into a dark brown mass. Bonnet called the granules 

 hrematoidin crystals, but Jenkinson was unable to demonstrate this 

 pigment in alcoholic extracts of the placenta. He found two other 

 pigments, one absorbing a small part of the violet end of the 

 spectrum, and the other showing two absorption bands, which 

 differed slightly from those of oxyhaemoglobin in neutral solution 

 and of haematoporphyrin in acid solution. This pigment is obviously 

 a haemoglobin derivative, and from it bilirubin may be formed. It 

 is present in the sheep and cow during pregnancy, but not in the 

 virgin uterus of the sheep. A similar yellowish -brown pigment 



they are, indeed, found at the bases of the villi, just where these extravasations 

 occur. Large allantoic bodies impregnated with calcium oxalate are found in 

 the horse'.' (see Fig. 101 above). 



