428 THE PHYSIOLOGY OF REPRODUCTION 



function as a protection against the attack of the foetal ectoderm has 

 already been mentioned. At the end of pregnancy their defence 

 is no longer required, as the trophoblast has also lost its activity. 



Iron Metabolism. The decidual cells are concerned in the 

 metabolism of iron, fat, and glycogen for the foetus. In the 

 rabbit, as contrasted with Ruminants, the ingestion of healthy 

 or degenerated erythrocytes probably does not occur. Though 

 Maximo w states that they are " present in the plasmodium," 

 they appear to be in the plasmodium only as the isolated penin- 

 sulae of decidual cells are in it, i.e. they lie in spaces surrounded 

 by trophoblast. Whether haemoglobin as such, or its more 

 immediate derivatives in the form of organic iron compounds 

 are absorbed has not been investigated, but Chipman has shown 

 that inorganic iron compounds are present, and their distribution 

 speaks for their absorption by the trophoblast. The compounds 

 appear as blue-black granules in sections stained with a weak 

 watery solution of haematoxylin. At the fourteenth day they 

 are present in the foetal mesoblast, especially where it approaches 

 the decidua. They increase in size and number for a few days 

 and then diminish, but some are still seen at the end of preg- 

 nancy. A few granules appear in the trophoblast between the 

 sixteenth and twentieth days (Fig. 103). From the sixteenth 

 day they are also found in an increasing number of the decidual 

 cells which lie close to the foetal placenta ; after the twenty- 

 fourth day, when the cells degenerate, the granules are no 

 longer discrete, but there are irregular blue-black patches up to 

 the end of pregnancy. 



Such isolated data cannot be accurately interpreted. The 

 fact that the deposits in the three tissues are always situated in 

 apposition to each other speaks for their absorption by the 

 foetal tissues ; on the other hand, a very small number of 

 granules are present in the trophoblast, and only for a few days. 

 It is possible that organic iron compounds, not shown by the 

 haematoxylin stain, are absorbed and broken up, and later 

 appear as granules in the mesoderm. Their further course to 

 the foetal liver, in which they are stored, has not been traced. 

 It is to be noted that the iron compounds are not only derived 

 from haemoglobin. They may also represent degeneration pro- 

 ducts of the nucleoproteins. 



