16 RESPIRATORY EXCHANGE OF ANIMALS AND MAN 



duction of an animal into the respiration apparatus, should be rigorously 

 adhered to. The behaviour of an animal just after it has been handled 

 and transferred is never normal, but becomes so only after a certain 

 time, differing greatly of course with different animals. As pointed 

 out by Krogh [1908], most respiration apparatus require also a certain 

 period of accommodation, especially with regard to temperature, 

 and serious sources of error in the determination itself are excluded 

 by beginning the experiment some time after the introduction of the 

 animal. 



A second important principle is to make sure that the quantities 

 determined are the same as those which it is desired to know. In 

 metabolism experiments it is generally desired to know the quantity 

 of oxygen used up in oxidations within the body during a certain time 

 and the corresponding quantity of carbon dioxide produced, but what 

 is determined is the quantity of oxygen absorbed into the body and 

 the quantity of carbon dioxide exhaled from it. The store of oxygen 

 within the body is so small and varies so little that the variations can 

 almost always be disregarded, but with the carbon dioxide it is very 

 different as there is a large store of loosely combined CO 2 both in the 

 blood and in the tissues. Great care has therefore often to be 

 exercised. An increased ventilation of the lungs will often wash out 

 a considerable proportion of the stored CO 2 by lowering the alveolar 

 tension of the gas, and it will then be replenished at some later occa- 

 sion. A change in the reaction of a tissue cannot fail to influence its 

 store of carbon dioxide, and the influence may possibly be large enough 

 to vitiate the results of determinations of the respiratory exchange. 

 A change in the body temperature finally will affect the solubility of 

 carbon dioxide in the fluids of the body and probably also their affinity 

 for the gas. 



The limits between which the amount of carbon dioxide stored in 

 the body may vary are unknown. 1 In an experiment on a rabbit 

 weighing 1800 gr., at least 250 c.c. CO 2 were washed out from the 

 body in excess of the production by artificial ventilation of the lungs 

 during 1*5 hours. The observed respiratory quotient remained above 

 unity all the time, rising to i'8 at last, and the quantity washed out 



1 In a series of experiments which will shortly be published in " Skand. Arch. Physiol." 

 Liljestrand has found that men of 60 kg. may wash out as much as 3-4 litres CO 2 during 

 30-40 minutes by increasing the ventilation from the normal to 13 litres per minute. A de- 

 crease of i per cent, in the alveolar CO g tension corresponds to a surplus elimination of i 

 litre CO 3 or a little less. 



