RESPIRA riO. Y 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 lias been stated to 
have a greater percentage of oxygen than that present in the atmosphere. 
Thus Bischof ' found 23 '-475 volumes per cent, as the mean of four analyses, and 
Dulk - obtained in one case 25*26, in another case 2G*77 per cent, of oxygen. 
Hufner, 3 however, has repeated and extended these observations, and found 
the following composition in the air removed from twelve. eggs, uhlncubated, 
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 Eespieatiox 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 6 of oxygen in 1774, Priestley ' 
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 m^ohie 
1 Jovm. f. Chem. u. Phys., Xiirnberg, 1S23, Brl. xxx. S. 446. 
- Ibid.. Halle, 1830, Bd. lviii. S. 363. 
s Arch', f. Physiol., Leipzig, 1892, S. 467. 
4 Peinbrey, Gordon, and Warren, Journ. Physiol., Cambridge and London, 1894, vol. 
xvii. p. 331 ; Pembrey, ibid., 1895, vol. xviii. p. 361. 
5 Preyer, "Specielle Pbysiologie des Embryo," Leipzig, 1885. 
6 Mayow can rightly claim to have discovered oxygen before 1674. See his "Tractatus 
cpiincjue." 
7 "On Air," vol. ii. p. 162. 
8 Mem. Soe. Boy. Med., 1782, tome hi. p. 576 ; Hist. Acad. roy. </. .•>•■.. Paris. 1789, p. 573. 
y "Minutes of a Society, etc.," London, 1795, p. 144. 
10 it Physiologie," Paris, 1806, 2nd edition, tome iii. p. 59. 
11 " On Factitious Airs," Bristol, 1796, part i. p. 13. . M "Researches," p. 439. 
13 Phil. Trans., London, 1808, pp. 266 and 280 ; 1809, pp. 415 and 427. 
