DEVELOPMENT. 677 



blood, are bathed or soaked in maternal blood contained in the uterine 

 sinuses. The arrangement may be roughly compared to filling a glove 

 with foetal blood, and dipping its fingers into a vessel containing mater- 

 nal blood. But in the foetal villi there is a constant stream of blood 

 into and out of the loop of capillary blood-vessels contained in it, as there 

 is also into and out of the maternal sinuses. 



It would seem that, at the villi of the placental tufts, where the foetal 

 and maternal portions of the placenta are brought into close relation 

 with each other, the blood in the vessels of the mother is separated from 

 that in the vessels of the foetus by the intervention of two distinct sets 

 of nucleated cells (Fig. 465). One of these (b) belongs to the maternal 

 portion of the placenta, is placed between the membrane of the villus 

 and that of the vascular system of the mother, and is probably designed 

 to separate from the blood of the parent the materials destined for the 

 blood of the foetus; the other (/) belongs to the foetal portion of the 

 placenta, is situated between the membrane of the villus and the loop of 

 vessels contained within, and probably serves for the absorption of the 

 material secreted Vy the other sets of cells, and for its conveyance into 

 the blood-vessels of the foetus. Between the two sets of cells with their 

 investing membrane there exists a space (d), into which it is probable 

 that the materials secreted by the one set of cells of the villus are poured 

 in order that they may be absorbed by the other set, and thus conveyed 

 into a foetal vessel. 



Not only, however, is there a passage of materials from the blood of 

 the mother into that of the foetus, but there is a mutual interchange of 

 materials between the blood both of foetus and of parent; the latter sup- 

 plying the former with nutriment, and in turn abstracting from it ma- 

 terials which require to be removed. 



Alexander Harvey's experiments were very decisive on this point. The 

 view has also received abundant support from Hutchinson's important 

 observations on the communication of syphilis from the father to the 

 mother, through the instrumentality of the foetus; and still more from 

 Savory's experimental researches, which prove quite clearly that the 

 female parent may be directly inoculated through the foetus. Having 

 opened the abdomen and uterus of a pregnant bitch, Savory injected a 

 solution of strychnia into the abdominal cavity of one foetus, and into 

 the thoracic cavity of another, and then replaced all the parts, every 

 precaution being taken to prevent escape of the poison. In less than 

 half an hour the bitch died from tetanic spasms; the foetuses operated on 

 were also found dead, while the others were alive and active. The ex- 

 periments, repeated on other animals with like results, leave no doubt of 

 the rapid and direct transmission of matter from the foetus to the mother 

 through the blood of the placenta. 



The placenta, therefore, of the human subject is composed of &fcetal 

 part and a maternal part, the term placenta properly including all that 



