FCETAL NUTRITION: THE PLACENTA 403 



connective tissue cells aaid are of use only as pabulum to be 

 absorbed by the ovum. But during the whole of pregnancy, as 

 mentioned above, there exist in the placenta decidual cells which, 

 in their appearance and staining properties, show no resemblance to 

 degenerated cells. From their abundance and great specialisation 

 they have in all likelihood definite functions to perform. Their first 

 formation dates from the destruction of the surface epithelium when 

 the blastocyst comes in contact with the connective tissue, and the 

 earliest to appear are in the neighbourhood of the ovum. Their 

 position and general appearance in different orders suggested to 

 Turner a maternal reaction against the advance of the parasitic ovum, 

 and the same idea has been forced on different observers. FothergiU ^ 

 speaks of the decidua preventing the injurious invasion of the uterine 

 wall by the foetal elements. Chipman's^ figures of the placenta of 

 the rabbit show that the ectoplacenta advances more rapidly where 

 it encounters a vessel than where it lies against decidual cells. Wade 

 and Watson^ have noted its resemblance to young granulation 

 tissue in the mucosa of the Fallopian tube in an early ectopic 

 pregnancy, Bryce and Teacher,* in their description of the youngest 

 human ovum yet examined, say : " The decidua formation is a process 

 of a conservative nature, by which, during the early months of 

 pregnancy, the activities of the trophoblast are limited and controlled 

 until such time as placentation is complete." Whether or not the 

 decidua forms the protection to the mother,' there is increasing 

 evidence that the trophoblast does not invade the decidua to the 

 extent supposed by the older authorities. This was first emphasised 

 by Hubrecht in the hedgehog, and has more recently been advocated 

 by Webster, and by Bryce and Teacher, in man. 



Hoffmann^ and Ahlfeld^ considered the decidua to be of the 

 nature of a diffuse gland whose celjs secreted a nutritive juice for 

 the wants of the foetus. They stated that they could demonstrate 

 such a secretion in the " iatervillous " spaces formed by the separation 

 of the decidual cells ; but their observations have been discounted by 

 the investigations of Werth,^ who showed that the spherical globules 

 described by Hoffmann were never present in the fresh placenta, but 



1 FothergiU, "Decidual Cells," Edin. Med. Jour., vol. v., 1899. 



2 Chipman, " Observations on the Placenta of the Babbit, etc.," Edin. Roy. 

 Coll. Phys. Labor. Rep., vol. viii., 1903. 



3 Wade and Watson (B. P.), " The Anatomy and Histology of an Early Tubal 

 Gestation," Jotir. of Ohstet. aniid Qynec. of the Brit. Emp., 1908. 



■• Bryce and Teacher, Contributions to the Study of the Early Development and 

 Imbedding of the Human Ovum, Glasgow, 1908. 



* Hoffmann, " Sicherer Nachweis der sogennanten TJterinmilch beim Men- 

 schen," Zejtsch. f Oeburtsh. u. Oyniik., vol. viii., 1882. 



" Ahlfeld, Berichte u. Arbeiten aus der geburtsh. Klinik zu Giessen, Leipzig, 

 1883. 



' Werth, "Beitrage zur Anatomie, Physiologie, und Pathologic der mensch- 

 lichen Schwangerschaft," Arch.f. Oynak., vol. xxii. 



