46 ORGANISM AND ENVIRONMENT 
In CO poisoning there is usually only a small per- 
centage of CO in the air, and as the haemoglobin of 
the blood has a large capacity for CO it takes a con- 
siderable time for enough CO to accumulate in the 
blood to cause dangerous symptoms. These symp- 
toms, however, come on in exactly the same insidious 
manner as those from oxygen want arising in any 
other way. The headache, nausea, etc., of CO poison- 
ing are the same as those of mountain sickness, and 
the more remote nervous, cardiac, and other after- 
symptoms of CO poisoning or serious oxygen want 
produced in any other way are due to damage result- 
ing from oxygen want, and to no other cause. The 
oxygen want produces not merely temporary func- 
tional effects, but structural changes in the cells of 
nervous and other tissues. 
As CO in small but extremely dangerous propor- 
tions in air cannot be detected by smell or by a lamp, 
I introduced, as a test for it, the use of a small warm- 
blooded animal, such as a mouse or canary. A small 
animal has an enormously greater respiratory ex- 
change and circulation rate than a man; and in con- 
sequence its blood becomes saturated with CO far 
more quickly. By watching the animal a miner can 
tell in good time whether he is in a dangerous atmos- 
phere, though in the long run the animal is not more 
sensitive to CO than the man. The provision of small 
animals for testing purposes at mines in Great Britain 
was made obligatory by recent legislation. 
Yandell Henderson discovered that after excessive 
artificial respiration on animals the breathing does 
