CHAP, ii.] PEEGNANCY AND BIRTH. 387 



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 considerable 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 

 foetus. 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 

 substance 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 foetus 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 foetus to 

 the mother, we have to deal with something more than ordinary 

 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, and if so how, to these and other questions which 

 suggest themselves no very satisfactory answer can at present be 

 given. With regard to fat, leaning on the analogy of the conclusion 

 at which ( 542) we arrived, that in the adult the fat of the food 

 is probably not taken up by the tissues as fat during the nutrition 

 of the tissues by the blood, we may perhaps suppose that the 

 mother does not supply the foetus with fat as such. We have 

 already referred to the significant presence of glycogen in the 

 placenta; and it would almost seem as if the placenta exerted at 



