730 THE RESPIRATION AND [pt. m 



knowledge of the biophysics and biochemistry of the embryo at the 

 present time so great as this. 



Various investigations have been made of closely related subjects. 

 The question of the initiation of pulmonary respiration, for instance, 

 was thoroughly gone into by Preyer and by Bert. The passage of 

 gases through the placenta was studied by Dubois & Regnard, by 

 Butte and by Charpentier & Butte, who from clinical experience and 

 a few experiments with rabbits supported Zuntz's original view that 

 in maternal asphyxia the foetal can give up oxygen to the maternal 

 circulation. In 1880 Hoeyghes reported that carbon monoxide would 

 not pass the placenta, but this was shown to be incorrect by Grehant 

 & Quinquaud and Plottier and, later, Nicloux and Nicloux & Baltha- 

 zard, examined the passage of carbon monoxide across the placental 

 membranes in the guinea-pig. They concluded that it passed through 

 by a diffusion process provided that sufficient time could elapse for 

 the slow dissociation of the carboxyhaemoglobin to create an adequate 

 pressure gradient at the placental membrane. It then appears in the 

 blood of the embryo, but, if the carbon monoxide is given in too great 

 amount, death of the animal occurs before these events have had 

 time to happen, and no carbon monoxide is to be found in the foetal 

 blood. Huggett later investigated, in some careful experiments, the 

 question of the passage of oxygen and carbon dioxide through the 

 goat placenta, measuring the partial pressures in the maternal and 

 foetal bloods with a view to deciding whether diffusion or secretion 

 held good. The results were as follows: 



Table 84. Embryonic blood-gases per cent, {average) . 



Sheep (Cohnstein 

 Goat (Huggett) & Zuntz) 



Carbon Carbon 



Oxygen dioxide Oxygen dioxide 

 Foetal arterial blood from umbilical vein 796 29-9 6-3 40-5 



Foetal mixed blood (going to brain) ... 5-90 36-6 — ~ 



Foetal venous blood from umbilical artery 2-94 41-4 2-3 47-0 



The blood-gas tensions were as follows (in mm. of mercury) : 



Goat (Huggett) 

 f ^ \ 



Carbon 

 Oxygen dioxide 

 Foetal arterial blood from umbilical vein 41 44 



Foetal mixed blood (going to brain) ... 28 54 



Foetal venous blood from umbilical artery 15 61 



Maternal arterial blood ... ... 60 43 



