FGETAL NUTRITION: THE PLACENTA 401 



support their theory by direct observation. Overlach l and Frommel 2 

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

 that the true origin is, as Creighton 3 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 4 demonstrated this 

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

 and Gulland. 5 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. 6 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 8 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 certain 

 animals, e.g. hedgehog (Hubrecht 9 ) and bat (Nolf 10 ), 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, " Beitrag zur Frage der Wachstumsrichtung der Placenta," Zeitsch. 

 f. (Jeburtsh. u. (tynak., vol. xxxvi. 



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

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



4 MasquelLn and Swaen, " Premieres phases du developpement du placenta 

 chez le lapin," Bull, de VAcad. roy. de Belg., 1879. 



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

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



6 Cf. Ulesko-Stroganoff, " Zur Frage von deni feinsten Bau des Decidua- 

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



7 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). 



8 Ercolani, " Sulla unita del tipo anatomico della placenta," Mem. delV Accad. 

 di Bologna, 1876. 



9 Hubrecht, " The Placentation of Erinaceus europ&us," Quar. Jour. Micr. 

 Science, vol. xxx., 1889. 



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

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



