104 DR. R. ANGUS SMITH PHYSIOLOGICAL EFFECTS OF 



a diminution in the amount of oxygen to the extent of ot 

 or even i per cent ? Liebig says, " In a closed space 8 

 feet long, 9 feet high, and 8 wide a man could not breathe 

 24 hours without uneasiness/^ This is equal to living 

 about 5 hours and a half in my lead chamber ; and in that 

 time, by sitting quietly, we may avoid uneasiness ; but the 

 air wiU be very bad, candles will scarcely burn, some wiU 

 go out, and any person entering suddenly will be very 

 unwell. The sensations are gradually affected, and nothing 

 striking is observed ; the senses are diminishing in power. 

 If we look at the important total acts, the circulation of 

 the blood and the respiration, we find that death has begun, 

 so to speak, and the life is going out as quietly as the 

 candle. 



Nearly all the usual experiments on breathing in impure 

 air have been made violently and not with small amounts of 

 impurity, and during a very long interval of time ; a rabbit 

 has been killed in a few minutes, and the same air has been 

 breathed until it has attained its maximum impurity. Lie- 

 big says, '^Lavoisier and Seguin found that the carbonic acid 

 of respired air, when again inspired, may be raised to 10 per 

 cent., but not beyond that amount, even when respiration 

 was continued, which it could be only for a very short 

 time. This proportion of carbonic acid may be regarded 

 as the limit at which life is endangered in man.'-* 



We can scarcely look on this experiment as sufficient. 

 I became distinctly faint in 4 per cent, of carbonic acid, 

 the others around me were very uncomfortable in even 

 less ; one fainted in 2 per cent., which did not affect my 

 senses. We can, when in very good condition, bear 4 per 

 cent, for a quarter of an hour at least, so that life is not 

 endangered suddenly ; but I am disposed to think that no 

 one could live long in such air. When hours are spoken 

 of, the danger to life of any amount less than this is not 

 immediate when the person is healthy. The constant 



