236 RESPIRATION. 



life ; small animals immersed in it, therefore, soon die as- 

 phyxiated. Pure hydrogen, too, can be breathed, but will 

 not support life ; it is either without effect on the economy, 

 or exerts a soporific influence. The experiments of many in- 

 quirers, however, have shown that cold-blooded animals, such 

 as frogs, can exist for hours in pure nitrogen and hydrogen ; 

 they become asphyxiated at length, and are apparently dead ; 

 but if not kept too long immersed in the gases, they recover 

 when brought into contact with the air of the atmosphere. 

 All observers, too, are agreed that these animals eliminate car- 

 bonic acid when confined in nitrogen and hydrogen. In a mix- 

 ture of four parts hydrogen and one part (volume) oxygen, 

 animals were found by Allen and Pepys to become sleepy, 

 without any prejudicial effect upon the health appearing to 

 ensue. Oxygen disappeared, and carbonic acid was evolved 

 precisely as when atmospheric air was breathed ; at the same 

 time, however, nitrogen made its appearance, and in such quan- 

 tity, too, that in the course of an hour the volume eliminated 

 equalled, and even exceeded by a half, the volume of the 

 animal which was the subject of experiment. Other gases 

 are true poisons to the economy carburetted, phosphuretted, 

 sulphuretted, arseniuretted hydrogen, &c. Air that contained 

 no more than 1-1 500th of its bulk of sulphuretted hydrogen 

 was sufficient to prove fatal to a bird ; 1 -800th destroyed a 

 dog, 1 -250th killed a horse. Some gases inspired in a state 

 of purity, or but little diluted, induce spasm and complete 

 closure of the glottis, and consequent, death ; more largely 

 diluted, they excite violent cough. To this list belong chlorine, 

 the vapour of iodine, nitric oxyde, ammoniacal gas, fluoboric 

 and fluosilicious gas, and the greater number of the strong 

 acid vapours, such as those of nitric acid, sulphuric and sul- 

 phurous acid, succinic acid, &c. The greater number of the 

 particulars related in the preceding paragraph have been made 

 known to us through the admirable researches of Sir 

 Humphrey Davy,]* 



395. The vivifying power of the air upon the blood is 

 due to its oxygen. If an animal be confined for a time in a 

 closed vessel, and the contained air be afterwards examined, 

 a considerable portion of its oxygen will have disappeared, 

 and another gas of a very different character, namely, carbonic 



* Dr. Julius Vogel, in Wagner's Physiology, p. 366. 



