238 



Comparative Animal Physiology 



will not be in this proportion, for ordinarily an oxygen debt develops which 

 must be liquidated alter the respiratory stress. Insects, which do not bifild up 

 much of an oxygen debt, may show respiratory excesses of 100 or more times 

 the resting rate."° 



The greatest metabolic increases with activity are those shown by insects 

 during flight-values as high as 90 liters of oxygen per kilo per hour having 

 been recorded for bees,^''^- -^^ and for the butterfly, Vanessa (Zeuthen, cited 

 by Krogh^'o), g^ increase of better than 100-fold (Table 41). Chadwick*'-' 

 ingeniously correlated wing movements with oxygen consumption in individu- 

 al Drosophila on flights of an hour or more. The oxygen consumption rate 



TABLE 41. OXYGEN CONSUMPTION OF SOME INSECTS 



DURING SIMULATED FLIGHT 



(Expressed in cc./gm./hr.) 



increases from 28 to 350 cu. mm./gm./min. to correspond with a wing rate of 

 1 1,000 strokes per minute. Only a small oxygen debt develops, and this is paid 

 off within two minutes after cessation of the flight. 



Various drugs can be applied to stimulate oxygen consumption in animals, 

 just as anaesthetics may be used to depress metabolic activity. Potent stimu- 

 lants are the compound dinitrophenol (DNP) and its derivatives, about which 

 a large literature has grown up. As an example of the stimulating capacity of 

 DNP one may cite the 342 per cent increase in rate of oxygen consumption 

 demonstrated by Bodine and Boell''-'' in grasshopper embryos during diapause. 

 Of interest in this connection is the work of Clowes and KrahF-- -"^ on Arhacia 

 embryos, which demonstrates that although the nitrophenols may stimulate 

 metabolism they inhibit cell division, thus emphasizing the polyphasic nature 

 and complexity of growth processes. 



Attempts to stimulate oxygen consumption by administration of endocrine 

 products have met with some interestingly conflicting results. It is well recog- 

 nized that thyroid extract, thyroxin, and thyroglobulin increase metabolic 

 activity in amphibians and mammals. However, this is not true for all verte- 

 brates. Fish do not respond with a clear-cut increase in metabolism after 

 thyroid feeding, '"'*• -^" and lampreys also fail to respond metabolically to 

 thyroid''^-'' -''* (see Chapter 22). 



The confinement of a number of animals together often stimulates them 

 into increased activity and oxygen consumption, but the opposite effect is 

 recorded for the goldHsh, in which the presence of company seems to depress 



