CHANGES DURING PREGNANCY 547 



normal pregnancy, which leads to an increased lung ventilation, may 

 be a physiological method by which the maternal organism adapts 

 itself to the presence of the foetus with its increased demand for 

 oxygen and its increased formation of COg. 



G. The Metabolism of Metals and Salts in PregTutn^y 



Little is known regarding the metabolism of the individual 

 metals and salts. The fixation of mineral elements is slight at the 

 beginning, but becomes active towards the end of pregnancy. From 

 first to last, about a hundred grammes are transferred from the 

 mother to the human foetus. "With a few exceptions, the mineral 

 salts are approximately in the same proportion throughout pregnancy. 

 The exceptions are sodium, potassium, and calcium, of which sodium 

 decrdases and calcium increases with the replacement of cartilage by 

 bone, and potassium increases with the increased manufacture of red 

 blood corpuscles (Hugounenq ^). 



The analyses of Oamerer and Soldener ^ of the ash of the^human 

 foetus have given the following results : — 



PA CaO NaaO K^O MgO FeA CI 

 38-5 36-1 9-1 7-8 0-9 O'S 7-7 



The significance of these figures lies in the preponderance of CaO 

 and PgOg in the ash. The analyses of Michel ^ and of Fehhng * of 

 embryos at different stages of development show that the retention 

 of mineral salts by the foetus does not proceed evenly. There is a 

 sudden increase, beginning in the twenty-ninth week, in the retention 

 of calcium from 0"4 gm. to 2 gm. and of phosphorus from 0"3 gm. 

 to 1'3 gm. These relations have been expressed very clearly in 

 graphs by HofFstrom.^ The relatively high retention of iron is also 

 significant. 



{a.) Iron. — Part at least of the iron for the foetus is derived from 

 the haemoglobin of the maternal organism. In the poly-cotyledonary 

 placenta of Ruminants and the zonary placenta of Carnivores, the 

 disintegration of red blood corpuscles has been depaonstrated. There 

 is less certainty regarding the actual ingestion of the red cells by the 

 syncytium of the discoid placenta, though it has been described by 



1 Hugounenq, " Eecherclies sur la statique des ^I6ments min6raux et 

 particulilrement du fer chez le foetus humain," Compt. Rend. Soc. Biol., 11th 

 series, vol. i., 1889. 



2 Camerer and Soldener, "Die chemische Zusammensetzung des neugeborenen 

 Menschen," Zeitsoh. f. Biol., vol. xxv., 1902. 



3 Michel, "Sur la composition de I'embrion et du foetus humain aux 

 difKrents 6poques de la grossesse," Compt. Rend, de la Soc. de Biol., vol. li., 1899. 



» Fehling, "Beitrage zur Phys. des placentaren Stoffverkehrs," ZeitscA. f. 

 Oynahol., vol. ii. 



' Hoffstrom, loo. cit. 



