496 



SCIENCE 



[N. S. Vol. XXV. No. ( 



be taken as the normal quantity which the 

 body requires, because, as Chittenden and 

 his school say, this amount is dictated by 

 habit and not by actual necessity. The 

 latter found, as stated before, that with a 

 proteid diet lower than the one employed 

 in the current diet of man, a number of 

 men continued their normal life without 

 special incidents. As a result of this ob- 

 servation these investigators assume that 

 the minimum proteid diet is the normal 

 one and advocate its adoption as a standard 

 diet. The finding that men can continue 

 to live with a certain minimum is a fact; 

 the assumption that this minimum is the 

 actual requirement of the organism, is, 

 however, only a theory, and a theory which 

 decides that in contrast to a human-made 

 machine the animal machine should be 

 provided with a minimum supply of energy 

 just sufficient for the average daily inci- 

 dents and daily work. 



Neither can we, on the other hand, look 

 upon the facts which were brought together 

 in this lecture as an absolute proof that 

 the animal's supply of energy ought also 

 to be provided on the same plan of super- 

 abundance. It may be claimed that the 

 animal's welfare is best cared for by ob- 

 serving stringent economy in the supply of 

 its energy. 



Luckily, however, the supply of oxygen 

 to the organism is a process practically 

 entirely independent of the will, and there- 

 fore a fact or two which we find here may 

 well throw some light upon our problem. 



One fact here is indeed instructive. It 

 is a frequently made and well established 

 observation that the oxygen of the inspired 

 air may be reduced to about one half of its 

 normal amount without causing any ill 

 effects whatsoever. The oxygen of the at- 

 mospheric air amounts to about 21 per 

 cent., and it may safely be reduced to 

 about 11 per cent, or 10 per cent. Nature 

 then supplies oxygen to the animal body in 



an abundance amounting at least to twice 

 the maximum quantity which the normal 

 condition of life may require. 



Furthermore, even with an atmosphere 

 greatly reduced in oxygen the bodj^ is 

 capable of attending to work so strenuous 

 that it may cause a consumption of oxygen 

 perhaps five times the amount normally 

 used up during rest or light work. This 

 occurs, as was demonstrated in the interest- 

 ing experiments of Zuntz and his co-labor- 

 ers, in climbing mountains and carrying at 

 the same time considerable loads at alti- 

 tudes with a barometric pressure of Iras 

 than 500 millimeters of mercury. 



We should also remember another in- 

 structive and characteristic fact, namely, 

 that the venous blood is comparatively rich 

 in oxygen, possessing often nearly two 

 thirds of that present in the arterial blood, 

 which means that the oxygen carried in the 

 arterial and capillary blood is greatly in 

 excess of the requirements of the cellular 

 tissues. 



Finally, another interesting point is that 

 labored breathing sets in long before the 

 tissues are in actual need of oxygen. Dys- 

 pnoeic breathing is a device to cause a 

 refilling of the exhausted surplus of oxy 

 gen by a more efficient pulmonary ventila- 

 tion. The hard-working skeletal muscles 

 which consume an undue amount of oxygen 

 produce at the same time a substance which 

 stimulates the respiratory center to greater 

 activity and thus to a more liberal provi- 

 sion of oxygen. This is again a sort of 

 self-repair of the loss to the factors of 

 safety. 



All this is sufficient evidence that as far 

 as oxygen is concerned the supply of the 

 body with energy is certainly not con- 

 ducted on the principle of stringent 

 economy. On the contrary, abundance is 

 the guiding rule here, as it is in the provi- 

 sions of the body's structures. 



We now again return to the question of 



