270 PHYSIOLOGY CHAP. 



It is certain that the exchange of material and energy in the 

 foetus is carried out under much more favourable conditions 

 than those in extra-uterine life. All the oxygen and histogenic 

 materials it needs are supplied to it by the blood brought by 

 the umbilical vein from the placenta, which represents, as Mayow 

 has well said, its respiratory and digestive apparatus. 



Zweifel (1876) was . the first to observe by opening the 

 abdomen of a pregnant rabbit, immersed in a bath of physio- 

 logical saline at 38, that if the foetus be carefully removed 

 without disturbing the umbilical vessels, the umbilical vein shows 

 the bright colour of arterial blood, whilst the blood of the 

 umbilical arteries is dark. Thus the foetal blood on its way 

 through the superficial capillary network of the villi of the 

 chorion takes up oxygen and gives off carbon dioxide by a process 

 similar to that occurring in the lungs, the foetal being separated 

 from the maternal blood circulating in the intervillous spaces 

 only by the thin walls of the vessels and by the epithelium of the 

 villi! The transudation of histogenic substances from the lacunae 

 of the villi to the vessels of the placenta is very active, corre- 

 sponding to the rapidity of foetal development. 



We have numerous experimental proofs that diffusible sub- 

 stances pass from the mother to the foetus. If sugar be injected 

 into the maternal vessels, it is found in large quantities in the 

 foetal tissues ; if atropine be injected into the mother, midriasis 

 is observed in the foetus (Thomas and Gillette) ; the foetus can 

 be killed by giving the mother strychnine, or even curare, which 

 has a weak degree of diffusibility. The following substances 

 given to the mother during the last stage of pregnancy are found 

 in the body and first urine of the new-born child : phosphorus 

 (J. Clouet) ; salicylate of soda (Benicke, H. Fehling) ; bromides, 

 ferrocyanides, potassium chloride (Porak); copper acebate (Philip- 

 peaux) ; iodide of potassium, tincture of iodine (Gusserow, 

 Krukenburg, Heidlen) ; and other medicinal substances. Certain 

 pathogenic germs also pass from the maternal blood to that of the 

 foetus a fact of great importance with reference to the genesis 

 of hereditary diseases. 



The process by which anabolic products pass from the mother 

 to the foetus and catabolic products from the foetus to the 

 mother is however certainly not one of simple diffusion. As a 

 matter of fact, the specific gravity of the foetal blood is greater 

 than that of the maternal. This difference proves that the 

 epithelial cells of the decidua and those of the placental villi 

 exercise a function similar to that of the intestinal epithelium. 

 The protein substances of the maternal blood probably undergo 

 some modification during their transmission to the foetus. We 

 do not know whether the fats of the maternal blood, which 

 Fehling thinks increase as pregnancy advances, are supplied to 



