1128 THE NUTRITION OF THE EMBRYO. [BOOK iv. 



699. Judging from analogy we may conclude that the food 

 of the foetus consists, like that of the adult, of proteids, fats, 

 carbohydrates and salts conveyed in water. In attempting to 

 understand how these materials pass, from the blood of the 

 maternal sinus to the blood of the foetal villus, we have to face 

 problems of the same kind as those which we met with in con- 

 sidering absorption from the alimentary canal ( 253). 



Here as there diffusion and filtration play their parts ; but 

 here also as there the passage of material does not follow the 

 laws of diffusion and filtration which regulate the passage of 

 material through non-living membranes. We have evidence 

 that diffusible substances pass readily from mother to foetus 

 and from foetus to mother. When sugar is injected in consid- 

 erable quantity into the vessels of the mother, it is found in 

 excess in the tissues of the foetus. When such a drug or poison 

 as atropin is injected into the mother it passes to the foetus, 

 and manifests its presence there by dilation of the pupils. Not 

 only may the foetus be killed by injection of strychnine into 

 the mother, but the mother may be killed by the injection of 

 strychnine carefully restricted to the fcetus. Again, if curare, 

 which is inert towards the foetus at least up to a certain dose, 

 be injected into the foetus, the mother is affected by the drug, 

 the fact that the drug does not poison the foetus assisting in 

 its transmission to the mother ; this result is especially worthy 

 of notice since curare has a very low diffusible power. The 

 influence of diffusion seems to be further illustrated by the 

 fact that if large quantities of sugar or other diffusible sub- 

 stance be .injected into the blood vessels of the mother, while 

 the thickened plasma of the maternal blood is diluted by the 

 entrance of water, as shewn by the diminished proportion of 

 red corpuscles, that of the fcetus as shewn by the same method 

 undergoes concentration ; water passes from the foetal blood to 

 meet the needs of the maternal blood. 



Nevertheless that in the passage of nutritive material from 

 the mother to the foetus, and of waste products from the fcetus 

 to the mother, we have to deal with something more than ordi- 

 nary diffusion, is shewn by the fact that the specific gravity of 

 the foetal blood differs from, being definitely above, that of the 

 maternal blood ; if diffusion had its full power the specific 

 gravities of the two bloods would soon become equalized. 

 Although exact information concerning the matter is at present 

 very limited or almost wholly wanting, it is probable that the 

 epithelium cells of the placenta, either those of the villi or the 

 ' decidual ' cells or both, play a part not unlike that played 

 by the epithelium of the alimentary canal or even play a more 

 important part. Whether the proteids of the maternal blood 

 undergo a change analogous to peptonification in passing to the 

 foetus, whether the mother furnishes fat to the foetal blood, 



