FCETAL NUTRITION: THE PLACENTA 399 



the investigations of His : ^ ' " They are not really specific tissue 

 structures, but tissue conditions requiring definite phases of proto- 

 plasmic vitality. They occur along with a high degree of activity— • 

 with increased absorption and action on material — as well as with 

 increased motility. Favourable conditions of nutrition form the 

 fundamental condition for the existence of syncytia, and such 

 conditions are certainly well offered in the uterus." At the present 

 time the syncytium is regarded as of the highest importance in 

 foetal nutrition. Strahl ^ and Heinricius,^ noting its gradual and 

 progressive diminution as pregnancy advanced, supposed that it 

 formed a part of the nutriment for the embryo, but this idea has 

 not been adopted. The general theory is that it is essential in 

 maintaining the interchange of material between mother and fcetus. 

 The substances necessary for the building up of the foetal body 

 may be divided into two groups — diffusible and non-diffusible. The 

 passage of the former can be explained by physical laws, but it is 

 different with the non- diffusible or colloid substances. This is a 

 difficulty which does not belong to the placenta alone, but to every 

 organ of the body, and authorities are divided between two theories, 

 the mechanical and the vital. The supporters of the mechanical 

 theory hold that all the processes occurring in the placenta are 

 possible by the laws of filtration and osmosis, and they have carried 

 out numerous experiments to prove that substances in solution may 

 pass across the placenta in both directions. Others, paying special 

 attention to the nature of the barrier formed by the epithelial 

 covering of the villi, deny that by such physical processes the non- 

 diffusible substances with large molecules, e.g. haemoglobin and other 

 blood proteins, can be absorbed by the syncytium. They postulate 

 a vital action on the part of the cells, by which the necessary 

 material is selected by the syncytium, and altered to a form in which 

 it may be transmitted to the foetal circulation. It is not yet settled 

 whether the activity of the syncytium is due to a phagocytic power 

 or to an enzyme action. 



There is a third theory regarding the transmission of nutritive 

 material from the mother to the foetus, viz. by the actual passage of 

 maternal leucocytes, charged with nutriment, from the one circulation 

 to the other. TThis theory was. first advocated by Eauber* as the 

 result of microscopic investigations, and he instanced, as further 



' His, " Die Umschliesaung der menschl. Frucht wahrend der f riihesten Zeit 

 der Schwangersohaft," Arch.f. Anat. u. Phys., Anat. Abth., 1897. 



^ Strahl, " Der Bau der Hundeplaoenta," Arch. f. Anat. %(,. Phys., Anat. Abth., 

 1890. 



2 Heinricius, " Ueber die Entwioklung und Struktur der Placenta beim 

 Hunde," Arch. f. mihr. Anat, vol. xxxiii., 1889. 



* Rauber, Ueber den Ursprung der Milch und die Erncihrimg der Frucht im 

 allgemeinen, Leipzig, 1879. Also Zool. Anz., No. 70. 



