RESPIRATION IN AIR 83 



gradually lapsing in about 15 minutes into the normal resting 

 type. The lowest curves marked Metabolism give the oxygen 

 absorption and corresponding C0 2 liberation in 3-minute 

 periods. Before the dive the gas exchange is fairly constant, 

 during the dive it is suspended, and just after there is a large 

 increase lasting for 7 periods (21 minutes) and covering in this 

 case 86% of the debt incurred during the dive. In most cases, 

 however, only about 1/2 of the debt is paid off in a compara- 

 tively short time, and it would appear that the seal is able to 

 extend the payment over a prolonged period during which the 

 metabolism is only slightly above normal. 



It is probably significant that the resting metabolism of seals 

 as determined both by Irving (1938) and by Scholander is 

 much higher than for mammals generally. Irving gives the 

 average figure 265 ml oxygen per min. for a seal of 29 kg which 

 is more than for a man of 70 kg, and Scholander's results 

 for the same weight vary from 200 ml to 300. There is reason 

 to suspect therefore that the basal level has not been reached 

 in the experiments, and it appears possible that an oxygen 

 debt can be paid off after a dive without any visible increase in 

 metabolism. 



The oxygen debt must be represented in the organism by 

 the accumulation of split products, of which lactic acid is the 

 best known, from the nutritional substances. In the upper 

 group of curves the results of sampling the arterial blood 

 before, during, and after the dive are summarized. It is 

 worthy of note that the oxygen in the blood falls to a very low 

 level and recovers within a minute. The lactic acid shows 

 only a slight rise during the dive and a very considerable one 

 after. This is a very significant fact to which we shall pres- 

 ently return. When the total lactic acid present in blood and 

 muscle at the end of a dive is figured out, which can be done 

 only very roughly, it is found to be of the order of 1 g per 

 minute of the dive, or more, which must afterwards be dis- 

 posed of by combustion and regeneration. The presence of 

 other split products cannot be excluded, but is not definitely 

 suggested by the results. 



