RESPIRA TION OF DIFFERENT GASES. 735 



In connection with the respiration of the embryo chick, it is interesting to 

 find that the air contained in the air chamber of the egg has been stated to 

 have a greater percentage of oxygen than that present in the atmosphere. 

 Thus Eischof l found 23*475 volumes per cent, as the mean of four analyses, and 

 Dulk 2 obtained in one case 25 '26, in another case 26*77 per cent, of oxygen. 

 Hiifner, 3 however, has repeated and extended these observations, and found 

 the following composition in the air removed from twelve eggs, unincubated, 

 and a few weeks old: Oxygen 18*94, nitrogen 79 '97, and carbon dioxide 1'09 

 volumes per cent.; and in the case of two goose eggs, incubated for sixteen 

 days, oxygen 19 '58 and 19*85, nitrogen 79*55 and 78*62, carbon dioxide 0*87 

 and 1*53 volumes per cent.; these eggs showed no trace of an embryo. 

 Experiments were also made upon the rate of diffusion of gases through the 

 egg-shell and the shell-membrane, and it was found that the rates of diffusion 

 of the different gases did not follow Graham's law ; they were not inversely 

 proportional to the square roots of the densities of the several gases. 



During the period of incubation of a chick the gradual development of the 

 power of heat regulation can be traced. At first the embryo responds to 

 changes in external temperature by a similar change in its respiratory ex- 

 change a fall of temperature causes a decrease, a rise of temperature an 

 increase, in the respiratory exchange ; then for a short time there is an inter- 

 mediate condition in which a change of temperature has no marked effect ; and, 

 lastly, when the chick is hatched, it responds as a warm-blooded animal. 4 



If tadpoles and larvae of salamanders (Salamandra maculata) be prevented 

 from coming to the surface of the water, their metamorphosis is greatly 

 prolonged, and if well fed they will live for a long time as purely aquatic 

 animals. 5 



THE EESPIRATION OF DIFFERENT GASES. 



Some gases, such as hydrogen and nitrogen, have no specific effect 

 when they are respired, and animals supplied with these gases alone die 

 simply from want of oxygen. Other gases, such as carbon dioxide, carbon 

 monoxide, nitrous oxide, and hydrogen sulphide, can be taken into the 

 lungs, and if present in sufficient quantity are absorbed, and produce 

 specific effects ; while a third class, such as ammonia and nitric oxide, 

 are irrespirable on account of their irritant action producing spasm of 

 the glottis. 



Oxygen. Soon after his re-discovery G of oxygen in 1774, Priestley 7 

 observed, both upon himself and upon animals, the effect of breathing 

 the pure gas ; in his own case he felt an agreeable facility of respiration, 

 and in animals he found that oxygen had a greater power than air in 

 supporting life. These experiments were repeated by Lavoisier, 8 

 Higgins, 9 Dumas, 10 Beddoes, 11 H. Davy, 12 Allen and Pepys, 13 and in some 



1 Journ. f. Chem. u. Phys., Niirnberg, 1823, Bd. xxx. S. 446. 



2 Ibid.. Halle, 1830, Bd. Iviii. S. 363. 



8 Arch. f. PhysioL, Leipzig, 1892, S. 467. 



4 Pembrey, Gordon, and Warren, Journ. Physiol., Cambridge and London, 1894, vol. 

 xvii. p. 331 ; Pembrey, ibid., 1895, vol. xviii. p. 361. 



5 Preyer, "Specielle Physiologie des Embryo," Leipzig, 1885. 



6 Mayow can rightly claim to have discovered oxygen before 1674. See his "Tractatus 

 qiiinque." 



7 "On Air," vol. ii. p. 162. 



8 Mem. Soc. Roy. Med., 1782, tome iii. p. 576 ; Hist. Acad. roy. d. sc., Paris, 1789, p. 573. 



9 "Minutes of 'a Society, etc.," London, 1795, p. 144. 



10 Physiologie," Paris, 1806, 2nd edition, tome iii. p. 59. 



11 "On Factitious Airs," Bristol, 1796, part i. p. 13. 12 "Researches," p. 439. 

 13 Phil. Trans., London, 1808, pp. 266 and 280 ; 1809, pp. 415 and 427. 



