SECTION 4 



THE RESPIRATION AND HEAT-PRODUCTION 

 OF THE EMBRYOi 



4-1. Early Work on Embryonic Respiration 



Probably the earliest examination of the respiration of embryos, 

 apart from mere opinions such as those of Fabricius ab Aquapendente, 

 was contained in the work of Spallanzani, who found that eggs gave 

 off and took in gases, although Robert Boyle in his Continuation of 

 New Experiments physicomechanical touching the Spring and Weight of the 

 Aire & their Effects had written in 1632, " I put Flies' Egs into an empty 

 receiver: no wormes were produc'd out of them". Nothing more 

 of importance was done till Coxe on May 19, 1794, presented to the 

 Academy of Sciences in Philadelphia An inaugural Essay on Inflamma- 

 tion, in which he stated that "the portion of air which we always 

 find in one end of the hen's &gg is oxygenous gas". His essay is now 

 rare, so I have not been able to ascertain whether he regarded the 

 contents of the air-space as pure oxygen or as simply containing pure 

 oxygen among its constituents. Coxe thought that the air-space was 

 of great importance for the proper growth of the embryo. Two years 

 later, Hehl at Tubingen carried out similar work, using Fontana's 

 modification of Priestley's eudiometer. He concluded that the air 

 was the same as ordinary air. 



In 1 8 1 1 Paris made an examination of the physiology of the fowl's 

 tgg, which he communicated to the Linnean Society in London. 

 According to his analyses, the air-space of unincubated eggs con- 

 tained "pure atmospherical air", but after a development of three 

 weeks there was "an inquination with carbonic acid". For his time, 

 Paris held very advanced views about gaseous exchange in animals — 

 "Is it not probable", he said, "that the repeated suspirations of the 

 fatigued are instinctive exertions to procure a greater proportion of 

 oxygen by which their muscular energy may be revived?" The egg- 

 white, in Paris' view, was merely a defence against the cold. Then in 

 1822 Sir Everard Home made similar investigations, in the course of 

 which he submerged eggs in water and other liquids, and observed 

 that they would not develop, a result which he attributed to the 



1 Note: I mgm. COj = 0-51 c.c; i mgm. O.^ = 0-70 c.c. (at n.t.p.). 



