FOETAL NUTRITION: THE PLACENTA 369 



from the destruction of the surface epithelium when the blasto- 

 cyst 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. 

 Fothergill l speaks of the decidua preventing the injurious in- 

 vasion of the uterine wall by the fcefcal elements. Chipman's 2 

 figures on 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 3 have noted 

 its resemblance to young granulation tissue in the mucosa of 

 the Fallopian tube in an early ectopic pregnancy. Bryce and 

 Teacher, 4 in their description of the youngest human ovum yet 

 examined, say : " The decidua formation is a process of a con- 

 servative 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 5 and Ahlfeld 6 considered the decidua to be of 

 the nature of a diffuse gland whose cells secreted a nutritive 

 juice for the wants of the foetus. They stated that they could 

 demonstrate such a secretion in the " inter villous " spaces formed 

 by the separation of the decidual cells ; but their observa- 

 tions have been discounted by the investigations of Werth, 7 



1 Fothergill, " Decidual Cells," Edinb. Med. Jour., vol. v., 1899. 



2 Chipman, "Observations on the Placenta of the Rabbit," &c., Edinb. 

 Roy. Coll. of Physic. Labor. Rep., vol. viii., 1903. 



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

 Tubal Gestation," Jour, of Obstet. and Oynec. of the Brit. Emp., 1908. 



4 Bryce and Teacher, Contributions to the Study of the Early Development 

 and Imbedding of the Human Ovum, Glasgow, 1908. 



5 Hoffmann, "Sicherer Nachweis dor sogennanten Uterinmilch beim 

 Menschen," Zeite. f. Qeburtsh. u. Gyniik., vol. viii., 1882. 



6 Ahlfeld, Berichte u. Arbeiten aus der geburtsh. Klinik zu Qiessen, 

 Leipzig, 1883. 



7 Werth, " Beitrage zur Anatomie, Physiologic, und Pathologic der 

 menschlichen Schwangerschaft," Arch. f. Oyndk., vol. xxii. 



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