EXPERIMENTS and OBSERVATIONS on the EFFECTS produced upon ANIMALS by the RESPIRATION of NITROUS OXIDE.
I. Preliminaries.
The term respirable, in its physiological application, has been differently employed. Some times by the respirability of a gas has been meant, its power of supporting life for a great length of time, when repeatedly applied to the blood in the lungs. At other times all gases have been considered as respirable, which were capable of introduction into the lungs by voluntary efforts, without any relation to their vitality.
In the last sense the word respirable is most properly employed. In this sense it is used in the following sections.
Non-respirable gases are those, which when applied to the external organs of respiration, stimulate the muscles of the epiglottis in inch a way as to keep it perfectly close on the glottis; thus preventing the smallest particle of gas from entering into the bronchia, in spite of voluntary exertions; such are carbonic acid, and acid gases in general.[183]
Of respirable gases, or those which are capable of being taken into the lungs by voluntary efforts.
One only has the power of uniformly supporting life;—atmospheric air. Other gases, when respired, sooner or later produce death; but in different modes.
Some, as nitrogene and hydrogene, effect no positive change in the venous blood. Animals immersed in these gases die of a disease produced by privation of atmospheric air, analogous to that occasioned by their submersion in water, or non-respirable gases.
Others, as the different varieties of hydrocarbonate, destroy life by producing some positive change[184] in the blood, which probably immediately renders it incapable of supplying the nervous and muscular fibres with principles essential to sensibility and irritability.
Oxygene, which is capable of being respired for a much greater length of time than any other gas, except common air, finally destroys life; first producing changes in the blood, connected with new living action.[185]