Permeability of Placenta 



345 



fusion. Considering, however, all the evidence up to the present 

 time, it seems probable that even in man the placenta does 

 furnish some regulatory activity, while in some of the more 

 complex types this control is much more elaborate. 



These results with sodium ferrocyanide and iron ammonium 

 citrate considered in connection with those of Romer and Wis- 

 locki indicate the advisability of extending, as far as possible, 

 the investigation of each type of substance to as wide a group 

 of different placental barriers as possible. This seems especially 

 important in regard to those investigations involving the careful 

 chemical estimation of the normal constituents of maternal and 

 foetal bloods which so far have been studied chiefly in the human. 



168 (2128) 



Carbon dioxide and the HCO s ion as specific respiratory 



stimulants. 



By ROBERT GESELL. 



[From the Washington University School of Medicine, St. Louis, 



Missouri.] . 



It has been noted by Howell, Collip, Dale and Evans, the 

 author and others that the intravenous injection of sodium bi- 

 carbonate may act as either a respiratory or circulatory stimu- 

 lant, eliciting hypernea or a marked rise in the blood pressure. 

 Such injection obviously increases the hydrogen ion concentra- 

 tion of the blood and inasmuch as it produces a slight dilution, 

 it decreases the amount of carbon dioxide in the blood eliciting 

 the stimulation. The increased respiration is, therefore contrary 

 to the usually accepted laws of respiration. The only apparent 

 change in the blood which might elicit stimulation is the greatly 

 increased number of HC0 3 ions. Collip, therefore, suggests 

 that the HC0 3 ion exerts a specific stimulating action on the 

 respiratory center. 



We believe, however, that this anomalous result may be other- 

 wise explained. When the carbon dioxide is dissolved in water 



