FCETAL NUTRITION: THE PLACENTA 457 



vene between the two blood-systems. In the rabbit the glandular 

 secretion is still less important after attachment, and even the blind 

 ends do not secrete; throughout the placenta there is normal 

 circulating maternal blood in direct contact with foetal tissues, and 

 it serves both as nutriment and for the exchange of gases. In 

 addition, there are stationary blood extravasations which are engulfed 

 by the trophoblast, but they are subsidiary. Both in the dog and 

 the rabbit there is a marked formation of symplasma which may be 

 connected, as Bonnet suggested for the dog and Maximow for the 

 rabbit, with the slowing of the circulation in the placenta, or may 

 be the result of a trophoblastic influence. 



In the placenta of the rabbit there is one other difference which 

 marks it off from the placenta of Carnivores and links it with 

 Insectivores and man the connective tissue cells of the mucosa 

 form decidual cells. They assist to an important degree in the pre- 

 paration of nutriment for the embryo. They exercise a phagocytic 

 action on the neighbouring degenerated maternal tissues, glandular 

 remnants and fibrin, and so attain their greatest development, while 

 at the same time they become store-houses of fostal nutriment. At 

 a later period they degenerate and are absorbed by the trophoblast. 

 Their possible function as a protection against the attack of the foetal 

 ectoderm has already been mentioned. At the end of pregnancy 

 their defence is 110 longer required, as the trophoblast has also lost 

 its activity. The so-called " decidual cells " of the Carnivora are a 

 later and different formation. 



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 Maximow states that they are 

 " present in the plasmodium," they appear to be in the plasmodium 

 only as the isolated peninsula} of decidual cells are in it, i.c: 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 hsematoxylin. 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 pregnancy. A 

 few granules appear in the trophoblast between the sixteenth and 

 '5 A 



