160 RESPIRATION 



is not more than about 0.2 per cent of an atmosphere. The amount 

 of free oxygen which would go into solution in blood at the body 

 temperature with an atmospheric pressure of two atmospheres is 

 4.2 volumes per 100 cc. of blood, which is just about as much as is 

 ordinarily taken from the blood as it passes through the tissues 

 (see Chapter X). 



The mouse remained quite normal and seemingly unconcerned, 

 except that when it exerted itself in climbing up the jar it seemed 

 to become more easily tired than usual. Thus CO has no appreci- 

 able physiological action except that of producing anoxaemia. 

 It is, physiologically speaking, an indifferent gas, like nitrogen, 

 hydrogen, or methane, and, like these gases, only acts physio- 

 logically by cutting off the supply of oxygen. Its only specific 

 physiological action, so far as I am aware, is that it has a slight 

 garlic-like odor. It is not an "odorless gas" except to those who 

 are afraid even to smell it on account of the mythical properties 

 commonly attributed to it. Animals which have no haemoglobin 

 pay no more attention to CO than to nitrogen. I kept a cockroach 

 for a fortnight in an atmosphere consisting of 80 per cent of CO 

 and 20 per cent of oxygen, and it remained perfectly well. CO is 

 not oxidized or otherwise decomposed in the living body of any 

 animal. 20 It passes in by the lungs and passes out far more 

 rapidly than is generally supposed by the lungs, without there 

 being the smallest loss. For this and other reasons it is a most 

 valuable physiological reagent. 



The popular idea that CO remains for long in the blood is based 

 simply on failure to realize the nature of the symptoms which fol- 

 low severe or long-continued anoxaemia. In the light of present 

 knowledge it is childish to suppose that as soon as anoxaemia is 

 relieved a patient will recover, or that anoxaemia is in itself a 

 trifling matter if life is not immediately imperiled. If there were 

 only one clinical lesson derived from a perusal of this book, I hope 

 it would be that anoxaemia is a very serious condition, the con- 

 tinuance of which ought to be prevented if at all possible. 



The properties of CO as a poison can now in the main be under- 

 stood in the light of preceding chapters. As the molecular affinity 

 of haemoglobin for CO is enormously more powerful than its 

 affinity for oxygen, it is evident that a very small proportion of 

 CO in the air is capable of saturating the blood to a noticeable 

 extent. The proportion of oxygen in dry alveolar air is about 14 



20 For experiments and references on this subject see Haldane, Journ. of PAysiol., 

 XXV, p. 225, 1899, and M. Krogh, Pfliiger's Archiv, 162, p. 94, 1915. 



