FCETAL NUTRITION: THE PLACENTA 401 



support their theory by direct observation. Overlach ^ and Frommel ^ 

 described them as modified glandular cells, but there is no doubt 

 that the true origin is, as Greighton^ first suggested, from the 

 interglandular tissue of the mucosa. This consists of connective 

 tissue of an embryonic type, which allows of a rapid transformation 

 of its cellular elements. Masquelin and Swaen* demonstrated this 

 mode of origin in Eodents, and were supported by Minot, and Hart 

 and GuUand.^ Leopold's studies of early ova showed that the same 

 origin was most probable in man, and Peters described in the mucosa 

 next the ovum connective tissue cells undergoing a decidual trans- 

 formation." Their first appearance in the superficial layers of the 

 mucosa has suggested a stimulus for their formation arising from 

 the product of conception.'' The study of early human specimens 

 has effectually disproved Ercolani's* idea that the uterine mucosa 

 was first entirely destroyed by the developing ovum, and then 

 replaced by decidual tissue formed from the cells of the vessel-walls. 

 Such an endothelial proliferation does, however, occur in certaiu 

 animals, e.g. hedgehog (Hubrecht ^) and bat (Nolf '•''), and probably in 

 ectopic gestation in man. 



The rapid increase in the size and number of the decidual cells, - 

 together with the dilatation of the blood-vessels, leads to a great 

 increase in the thickness of the serotina. At a certain stage it 

 reaches its full development, and then gradually diminishes till, at 

 the end of gestation, it forms only a thin layer> and even disappears 

 entirely at parts so that the villi impinge on the muscular wall. 



Individual decidual cells have probably a short life-history. 

 Even at a comparatively early period many of them are found in 



1 Overlach, " Die pseudomenstruirende Mucosa Uteri nach akuter Phosphor- 

 vergiftung," Arch. f. mikr. Anat., vol. xxxv., 1885. 



2 Frommel, " Beifcrag zur Frage der Wachstumsrichtung der Placenta," Zeitsch. 

 f. Gehurtsh. u. Qynalc., vol. xxxvi. 



3 Creighton, " The Formation of the Placenta in the Guinea-pig," Jour, of , 

 Anat. and Phys., vol. xii., 1878. 



* Masquelin and Swaen, " Premieres phases du developpement du placenta 

 chez le lapin," Bull, de I'Acad. roy. de Belg., 1879. 



^ Hart and Gulland, "On the Structure of the Human Placenta, etc.," Labor. 

 Rep., Roy. Coll. Phys., Edinburgh, vol. iv., 1892. 



" Cf. Ulesko-Stroganoff, " Zur Frage von dem f einsten Bau des Decidua- 

 gewebes, etc.," Arch.f. Oynak., vol. Ixxxvi., 1908. 



'' Under abnormal conditions the formation of , decidual cells occurs even 

 although no ovum is present in the uterus, e.g. in tubal pregnancy in the 

 human female. This indicates a chemical stimulus, probably from the corpus 

 luteum, effected through the blood-stream (see p. 368). Moreover, it is known 

 that decidual tissue is formed as a result of artificial or mechanical stimuli, 

 provided that an active corpus luteum is present in the ovary (see p. 374). 



^ Ercolani, "Sulla unita del tipo anatqmico della placenta," J/em.. delV Accad. 

 di Bologna, 1876. 



^ Hubrecht, "The Placentation of Erinaceus europmus," Quar. Jour. Micr. 

 Science, vol. xxx., 1889. 



'" Nolf, " Modifications de la muqueuse uterine pendant la gestation chez le 

 murin," Arch, de Biol., vol. xiv., 1896. 



