The next point to determine was the influence of the air upon the same animals exercising the respiratory function, and retaining their circulation, compared with those deprived of these functions. The difference of time in the two cases developes the influence which the general circulation of the blood, free from aërial contact, exercises upon the nervous system. To ascertain this point, an equal number of frogs, deprived of the power to exercise their respiratory and circulating functions, together with others left entire, were respectively plunged into disaërated water. At times the difference in favour of the untouched animals was twenty-four hours in favour of the duration of life. Similar trials with toads and salamanders produced the same results. In each case _asphyxy_ came on; but the existence of the animals which lived without the respiration and circulation was much shortened. Thus the relative powers of life between the sole and insulated action of the nervous system, and its action combined with the circulation of dark blood, were estimated. The inference to be deduced, therefore, is, that although disaërated blood furnishes but an ephemeral sort of existence, it nevertheless exercises a comparatively favourable influence upon the nervous and muscular systems, since it tends to the prolongation of the action of these animal functions. Dr. Edwards next proceeds to investigate the phenomena of _asphyxy_ produced by _strangulation_, or the mechanical obstruction to the access of air to the lungs, and consequently to the blood. The same animals were employed. When the windpipe was rendered impervious by ligature, the muscles of the animals seemed to be paralysed directly; and although their motions became subsequently revived at times, [p144] they never altogether recovered their perfect freedom. As a comparative illustration, an equal number of frogs were submersed in water, all of which died in about ten or eleven hours, while those which were strangled lived from one to five days. Salamanders continued active longest, and one did not cease to exist till the eleventh day, although during this time he was in a complete state of _asphyxy_ from perfect strangulation. Dumeril once found that a salamander lived a long time after decapitation, even when the cicatrix of the wound was healed so as to stop all access of air to the lungs. In comparing the effects of strangulation with those of submersion or drowning, it is to be supposed either that these animals exist a limited period without the necessity of the nervous system being in contact with atmospheric air, or that the air influences their blood through the integuments of the body. Accordingly Dr. Edwards put this to the test by making experiments upon _cutaneous respiration_.