AND ITS EFFECTS UPON ANIMAL LIFE. 3 



carbonic acid rises perceptibly in theatres, etc., tlie reduction of oxygen is quite 

 insignificant, and tliat the [)ropoi"tion rarel}' falls below 20 per cent. 



Regnault and Reiset, (3), in 1849, also found that when sufficient oxj^gen is 

 supplied to an atmosphere quite rich in carbonic acid, an animal can still live in it. 

 Fried lander and Herter (4) found that the breathing of an atmosphere containing 

 20 per cent, of carbonic acid for an hour produced no symptoms of depression, but 

 caused stimulation of the respiratoiy centres and an increased activity of the 

 heart. 



Claude Bernard (5), in 1857, ex[)erimented with animals confined in atnios- 

 pheiic air and in mixtures both richer and poorer in oxygen than atmosphei'ic air. 

 A small bird placed in a bell glass of a little more than two litres' capacity, containing 

 a mixture of 13 per cent, carbonic'acid, 39 per cent, oxygen, and 48 pei' cent, of 

 nitrosen, died in two and one-half hours. He demonsti'ated that carbonic acid is 

 not poisonous when injected under the skin of animals — as much as one litre 

 injected under the skin of a i-abbit producing no ill eft'ects. No ill eflfects followed 

 the injection of the gas into the jugular vein and into the carotid arterj^ An 

 atmosphere of equal parts of oxygen and nitrogen had no effect upon an animal 

 confined in it, while an atmosphere composed of equal parts of carbonic acid and 

 of oxygen produced inunediate death in the animal placed in it. He explains the 

 poisonous effects of carbonic acid when respired to be due to the fact that it 

 deprives the animal of oxygen. Similar results \vere I'eported by Valentin (6) 

 and by Paul Bert (7). 



Richardson, in 1860-61, (8), found that a temperature much higher or lower 

 than 20° C. had the effect of shortening very considerably the lives of animals con- 

 fined in an unventilated jar, and that these effects were more marked when the 

 animals were confined in an atmosphere i-icher in oxygen than air, iu which case 

 he found that by passing electric sparks from a frictional machine through the 

 fatal air (having previously deprived it of its carbonic acid) it was again made 

 capable of supporting life, from which he concluded that the oxygen is " devital- 

 ized " during respiration, and that the electric spark has the faculty of revital- 

 izing it. 



Von Pettenkofer, in 1860-63, (9), showed that the symptoms observed in 

 crowded ill-ventilated places were not pi-oduced by the excess of carbonic acid, nor 

 by a decrease in the proportion of oxygen in the air ; neither of these being suffi- 

 cient in our dwellings, theatres, etc., to produce toxic effects. He did not believe 

 that the irapui-e air of dwellings was directly capable of originating specific dis- 

 eases, or that it was really a poison in the ordinary sense of the term, but that it 

 diminished the capability of withstanding the influence of disease-producing agen- 



