422 PROCESSES INFERRED FROM INDIRECT OBSERVATION 



the emotions, differences in metabolism, differences in the use of nar- 

 cotics or drugs, and differences in activity are only some of the number 

 of variables which enter" (Loeb). Hence the attempt to compute the 

 temperature-coefficient of the heart-beat in situ in man from the 

 acceleration of the beat in Fevers is illogical, and we find, as a matter of 

 fact, a great deal of discordancy in the values computed from data of 

 this kind, coefficients varying from 1.8 to 5 having been reported. 



The Respiratory Rhythm is even more susceptible to modification by 

 sensory stimuli, muscular exertion and so forth, than the cardiac 

 rhythm, and consequently the coefficients which have been observed 

 for the rate of the respiratory movement at different temperatures are 

 not of so uniform a character as those which are cited above. Never- 

 theless the influence of temperature upon the Respiratory Center is 

 extremely striking. It has long been a familiar fact that warming the 

 blood in the carotid artery, by causing it to flow through a heated tube, 

 results in a marked acceleration of the respiratory rhythm, and in 

 frogs it has been shown that the direct application of heat to the floor 

 of the fourth ventricle leads to a very decided increase in the rapidity 

 of respiratory movements. It is an extremely interesting fact that the 

 effect of temperature upon the respiratory rhythm of cold-blooded 

 animals is very much greater at a low oxygen-tension than at a high, 

 possibly because when the oxygen-tension is low and the consumption 

 of oxygen by all of the tissues is accelerated by an elevation of tempera- 

 ture, the effect of the temperature elevation itself is aided by the 

 stimulation of the respiratory center which lack of oxygen indirectly 

 entails, while when oxygen is abundant there is sufficient for the needs 

 of all the tissues even at high temperatures, and the secondary stimula- 

 tion of the center does not occur. 



The influence of temperature upon the velocity of "Basal Metab- 

 olism" or tissue-respiration can only be studied in cold-blooded 

 animals under conditions which exclude muscular movement, which 

 would, of course, introduce irregular fluctuations in the rate of con- 

 sumption of oxygen. This problem has been approached by Krogh in 

 several ingenious ways. One method was to employ the pupae of 

 insects in which tissue-respiration is of course maintained but muscular 

 movement is arrested. The following were results obtained with the 

 pupae of the mealworm, Tenebrio molitor: 



Oxygen-consumption Temperature-coefficient 



lemperature. per kilogram-hour. per 10 C. 



10 43.5 5.7 



15 104. 3.2 



20 185. 2.6 



300. 2.2 



445. 2.2 



25. 

 30. 



32. 5 C 



529. 



It will be observed that the temperature-coefficient is very high at 

 low temperatures and falls rapidly as the temperature rises. A similar 



