194 PRACTICAL PHYSIOLOGY 



the output of carbon dioxide and the body temperature. This can 

 be observed in mice placed in a high-pressure chamber. A mouse 

 is affected with dyspnoea in 10 atmospheres of oxygen, goes into 

 convulsions and soon dies. In 50 atmospheres it is instantly killed. 



CHAPTER LIL 

 THE INFLUENCE OF CARBON MONOXIDE. 



CARBON MONOXIDE is a poisonous gas in virtue of its great affinity for 

 haemoglobin ; oxygen is displaced and carboxy haemoglobin is formed. 

 Unconsciousness, convulsions, and death are produced by the lack of 

 oxygen which arises when a large portion of the haemoglobin is com- 

 bined with carbon monoxide and thus deprived of its power of carrying 

 oxygen. 



Carbon monoxide is present as an impurity in coal-gas, and in water-gas, 

 which is often used in the adulteration of coal-gas, the percentage is a very 

 high one. It is due to this gas that death so often results from coal-gas 

 poisoning. In the air of mines after an explosion there is present a 

 large quantity of carbon monoxide, due to the incomplete combustion 

 of coal dust ; miners overtaken by such a disaster generally die from 

 poisoning by this gas. 



DEMONSTRATION. A white rat or mouse is selected for the experi- 

 ment, for it is easier in such animals to see in the snout and feet the 

 change of colour due to the formation of the carboxy haemoglobin. The 

 animal is placed under a glass bell jar and coal-gas is admitted ; it 

 becomes restless, unconscious, convulsed, and dies within a few seconds. 

 This is one of the quickest methods of killing an animal, and has the 

 advantage that it rapidly produces unconsciousness. 



If the animal be removed to free air at the beginning of the stage of 

 unconsciousness it may recover. The carboxyhaemoglobin is gradually 

 dissociated and oxyhaemoglobin is formed in its place. In rabbits this 

 occurs very rapidly ; the animal quickly recovers, passing through a 

 stage of incoordination. 



Haldane has shown that the best indicator of the presence of poison- 

 ous doses of carbon monoxide is a small warm-blooded animal, such as a 

 mouse or bird, which is affected, owing to its rapid respiratory exchange, 

 much sooner than a man. This method has been employed with success 

 by rescue parties entering a coal mine after an explosion. 



The colour of the snout and feet of the white mouse or rat killed by 

 carbon monoxide is pink or cherry red. The blood in the viscera has a 



