142 Dr. Edwards, De V Influence 



tion, explainiilg tlie action of the air upon animals physio- 

 logically. 



In this inquiry warm-blooded animals were almost exclu- 

 sively referred to. 



Spallanzani certainly investigated the action of the air on 

 animals of cold blood, but less in relation to the three grand 

 objects of Bichat and Le Gallois ; and Spallanzani had the 

 misfortune to live in an age when neither chemistry nor 

 physiology had made such advances as the present age has 

 produced. ' 



. Messrs. Humboldt and Provencal have, indeed, supplied 

 much of this deficiency, by their researches into the respira- 

 tory functions of fishes. Nevertheless, the ground was still 

 open, and our author has justly appreciated the extent of 

 former inquiries, and observed that the phenomena of cold- 

 blooded animals were too extraordinary to be noticed lightly, 

 and required much more extensive observation than was 

 previously bestowed upon them. With this impression, he 

 proceeded to form an estimate of the comparative influence 

 of the air and water upon the nervous and muscular systems 

 of cold-blooded animals, which the singular modifications of 

 life among reptiles in particular afford ample means of 

 ascertaining. 



We know that these animals possess the extraordinary 

 property of existing a considerable time after the removal of 

 the heart, with the free exercise of their senses and of volun- 

 tary motion, notwithstanding the suppression of the circula- 

 tion. Dr. Edwards accordingly selected salamanders for his 

 first investigations, and removed the heart, with the bulb of 

 the aorta. Two of these were exposed to the free action of 

 the air, and the other two were submersed in water previously 

 deprived of air by boiling ; a similar temperature being 

 maintained in each medium. In four or five hours those 

 submersed in the non-areated water ceased to be active, 

 unless irritated, when they still appeared to retain voluntary 

 power. One died in eight, and the other in nine hours. 

 The salamanders in air lived from twenty to twenty-six hours 

 and upwards. These comparisons were frequently repeated, 

 and upon frogs and toads, with the same results, showing 

 the experiments in air to be far more favourable to their 

 existence than with the animals submersed in the water. 

 Eight hours were about the maximum of the duration of life 

 among the animals submersed in the water, and twenty-nine 

 among those exposed to the air; so that, independently of 

 ^respiration, the air is thus proved to be the most proper 



