GENERATION AND DEVELOPMENT. 269 



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. 428). 

 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 des- 

 tined for the blood of the foetus; the other (/) be- 

 longs to the foetal portion of the placenta, is sit- 

 uated between the membrane of the villus and the 

 loop of vessels contained within, and probably 

 serves for the absorption of the material secreted 

 by the other sets of cells, and for its conveyance FlG 433. Extremity of a 

 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 ^ t^uu^V cefis n of 

 absorbed by the other set, and thus conveyed into ^^^^i^Soa^) 10 ^ 

 the foetal vessels. 



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 

 materials 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 impor- 

 tant 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 precau- 

 tion 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 experi- 

 ments, 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 a foetal 

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

 entanglement of foetal villi and maternal sinuses, by means of which the 

 blood of the foetus is enriched and purified after the fashion necessary 

 for the proper growth and development of those parts which it is designed 

 to nourish. 



