734 



CHEMISTR Y OF RESPIRA TION. 



In 1834, Theodor Schwann l showed that, when hens' eggs are kept at a 

 warm temperature in gases containing no oxygen, the germinal membrane 

 enlarges, and the area pellucida is formed, but no embryo ; eggs would develop 

 normally in warm air, after they had been in hydrogen for twenty-four hours at 

 a warm temperature, but not if the exposure to hydrogen had lasted thirty 

 hours or more. 



The first determinations of the respiratory exchange in eggs are due to 

 Baudrimont and Martin Saint- Anges, 2 who showed that the eggs of birds and of 

 snakes gave off carbon dioxide during incubation, and that the embryos of 

 frogs died if placed in water free from air. The quantitative results obtained 

 by these observers are not trustworthy, owing to the defective methods of gas 

 analysis then in use. The first reliable determinations are those made by 

 Baumgartner 3 throughout the period of i^ubation of hens' eggs. The follow- 

 ing table gives some of the results : 



Similar experiments were made by Pott and Preyer, 4 who found that a fertile 

 egg, weighing 50 grms., lost in weight about 10*27 grms. during incubation, an 

 unfertile one 9 '70 grms., and an egg kept at the temperature of an ordinary 

 room 1*66 grms., in twenty -one days. The respiratory exchange of a developing 

 embryo in an egg weighing 50 grms. was, for periods of twenty-four hours : 



Pott 5 also showed that the development of the embryo is not hastened or 

 delayed if the egg is incubated in an atmosphere of oxygen. During incuba- 

 tion, it has been proved that the temperature of the embryo, owing to its meta- 

 bolism, is slightly warmer than the temperature of its surroundings. 6 



1 Arch.f. Anat., Physiol. u. wissensch. Med., 1835, S. 121. 



2 Compt. rend. Acad. d. sc., Paris, 1843, tome xvii. p. 1343 ; Ann. de chim. et phys., 

 Paris, 1847, Ser. 3, tome xxi. p. 195. 



3 " Der Athmungsprozess im Ei," Freiburg im B., 1861. 



4 Arch.f. d. ges. Physiol., Bonn, 1882, Bd. xxvii. S. 320. 



5 Ibid,, 1883, Bd. xxxi. S. 268. 



6 Barensprimg, Arch. f. Anat., Physiol. u. wissensch. Med., ]851, S. 126. See also 

 " Animal Heat," this Text-book, vol. i. 



