AND PREGNANCY. 373 



vcred at the Dublin Lying-in-Hospital, and the proportion of 

 women producing twins or more is about 1 in 57. 

 The proportion of males to females, about 10 to 9.* 

 (E) Fourcroy is almost the only author who has examined 

 the blood of the foetus, f and his Observations, Berzelius re- 

 marks, " seem to have been made by chance, and not to be de- 

 duced from any experiment ■" " credible authors have asserted 

 that the eye cannot distinguish between the arterial and venous 

 blood of the foetus." % Bichat could observe no difference in 

 the arterial and venous blood of the umbilical chords of several 

 guinea-pigs examined while the mother's respiration was still 

 continuing after an opening had been made into the abdomen, 

 " — les deux sangs offroient une noirceur egale." § So too in 

 regard to dogs. || 



The chick, nevertheless, in the egg, cut off from all intercourse 

 with the mother, requires its blood to be purified by the external 

 air : for if the shell is varnished, the chick dies ; and if, during 

 the latter half of incubation, the shell is carefully opened, the 

 chorion, to use the language of Blumenbach, presents one of the 

 most splendid spectacles in the organic creation ; the arteries are 

 seen carrying blood of a bright scarlet, and the veins of a livid 

 red.** The foetus of the kangaroo has no vascular connection with 

 the mother, being surrounded by a kind of jelly, and is supplied 

 with external air by tubes opening into the. uterus from within, 

 for this express purpose. 



* John Cross, Sketches of the Medical Schools of Paris, p. 192. 



•f Annates de Chimie. T. vii. p. 162. 



X Animal Chemistry. Translation, p. 41 sq. 



§ Rickcrchcs Physiologiques. p. 27 1 . 



|| Anatomie Ginirale. T. ii. 344. 



** Comparative Anatomy. Translated by Mr. Lawrence. § 372. 



