102 VITALITY AND EFFICIENCY WITH RESTRICTED DIET. 



the universal respiration apparatus when applied to muscular work 

 experiments, but they are best used with a ventilation of approximately 

 45 to 50 liters per minute. Hence the orifice leading into the sampling 

 cans was made of such size (10 mm. in diameter) as to allow the escape 

 of approximately 45 to 50 liters of air per minute through it. Thus, by 

 connecting to the sampling can a suction pipe leading to a positive 

 blower run by an electric motor, air at the rate of 45 liters per minute 

 could be withdrawn, passed through suitable purifiers, and the carbon 

 dioxide in it collected in a soda-lime bottle, as is done with the uni- 

 versal respiration apparatus. The amount of carbon dioxide thus col- 

 lected obviously represents the total amount in the sample. 



Another factor in determining the size of the orifice leading into the 

 sampling can and the total amount of air to be taken care of by the 

 purifying device was that with these bottles, although the combined 

 weight of one soda-lime and one sulphuric-acid bottle is approximately 

 5,500 grams, it is necessary, to minimize errors in weighing, that not 

 less than 2.5 to 3 grams of carbon dioxide should be absorbed. With a 

 ventilation of 45 liters per minute and the residual carbon dioxide 0.5 

 per cent, the amount absorbed would correspond to approximately 9 

 grams of carbon dioxide in a 20-niinute period. Even if the ventilation 

 were so adjusted as to have the carbon-dioxide content but 0.25 per 

 cent, the amount absorbed would be approximately 4.5 grams for a 

 period as short as 20 minutes. It is thus possible to use short periods 

 with the respiration apparatus, provided the production of carbon 

 dioxide is sufficient for the carbon-dioxide content of the residual air 

 to be at least 0.25 per cent. Obviously, if the total ventilation of the 

 group chamber could be reduced to but 45 liters per minute, the uni- 

 versal respiration apparatus itself would suffice for the absorption and 

 measurement of the carbon dioxide in the air, and we would have here 

 nothing but a magnified form of the clinical respiration chamber 

 developed and in use in this laboratory.^ 



But since the use of our large respiration chamber, with a volume of 

 44,000 liters, involves a much greater production of carbon dioxide 

 than the clinical respiration chamber, with a volume of but 600 liters, 

 a ventilation of 45 liters per minute would be inadequate for the removal 

 of the larger amount of carbon dioxide, because the ventilation of a 

 respiration chamber is dependent upon two factors (1) the amount of 

 carbon dioxide produced and (2) the percentage of residual carbon 

 dioxide desired. 



The main problems, therefore, in the aliquoting and analysis of this 

 air-current, are, first, to secure perfect aliquoting, and, second, to insure 

 constancy in both the amount and pressure conditions of the air dis- 

 charged ; finally, since the outdoor air entering the respiration chamber 

 contains a definite percentage of carbon dioxide, the calculation of the 



1 Benedict and Tompkins, Boston Med. Surg. Journ., 1916, 174, pp. 857, 898, and 939. 



