64 SCIENCE PROGRESS 



so would contain a constant percentage of oxygen even if its 

 haemoglobin did not become fully saturated. 



In fish, amphibians and snakes the attempt seems occasionally 

 to be made to maintain a temperature above that of the en- 

 vironment (i6a), but in how far it approaches to being constant 

 we only know for two specimens of the Indian python (13A). 

 It would be interesting to find out whether in a species of 

 Thynims, the bonito, which may have an internal temperature 

 as much above that of the environment as the python, it is 

 more nearly constant and how far the demand for oxygen 

 in the one and in the other varies both with the external 

 temperature and with the size of the individual ; moreover, 

 if it so varies, in what way the supply is regulated to meet 

 the different demands. 



The difference obtaining between the warm-blooded verte- 

 brates on the one hand and all the cold-blooded except fish 

 on the other, with regard to the relation of the oxygen to the 

 volume of the blood in the systemic circulation, is illustrated in 



A B 



Fig. I. — Diagrams to show the sort of relation of the oxygen to the blood-volume 



in the systemic circulation. 



A, warm-blooded vertebrate, b, reptile and amphibian. 



fig. I. Regulating the volume rate would regulate the oxygen 

 supply only with arrangement A. With any other arrangement, 

 such as that in B, the absolute amount of oxygen supplied in 

 unit time could be increased by increasing the frequency of the 

 beat, but it could not in that way be regulated at all accurately 

 to suit special demands.^ 



1 Since this paper went to press, Krogh has published a series of articles in 

 the Skand. Arch. f. Physiol. (1910) in which amongst other things it is shown 

 that a method of regulating the oxygen-supply to the body does exist in reptiles 

 and amphibians. This consists in adjusting the relative volumes of blood in the 

 pulmonary and systemic arches by alteration of resistance in the pulmonary 

 arteries efifected by variations in the tonus of their vaso-constrictor nerves. By 

 this means the blood per beat driven into the systemic circulation becomes less 

 in volume the more oxygen the tissues consume, but its oxygen-tension not only 

 relatively but absolutely greater, in consequence of the increase in the volume 

 going per beat through the lungs, involving as it does a greater absolute 

 absorption of oxygen. Although a convenient way of meeting differences of 

 oxygen-requirement in the individual, it is not one that would lend itself to 



