432 IV AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



settle this point by making three series of experiments : in one they injected 

 certain readily oxidizable substances into the blood; in another the substances 

 were injected into the stomach; and in another sulphate of sodium or other 

 purgative was given. When the substances were injected into the blood, Zuntz 

 and Mering found as a general result that the absorption of O was not increased, 

 while the formation of C0 2 was slightly increased ; when injected into the stom- 

 ach, no marked increase in respiratory activity occurred unless the substances were 

 given in large quantities. When, however, in addition to the readily oxidiz- 

 able substances, a purgative was injected, or when the purgative was given 

 alone, the absorption of O and the elimination of 0O 2 were considerably in- 

 creased. They were therefore led to conclude that the increased respiratory 

 interchange during digestion is due chiefly to the muscular activity of the 

 intestinal walls. Loewy 1 has confirmed this conclusion, and has clearly shown 

 that the increase in respiratory activity is chiefly related to the intensity of 

 peristalsis, the most marked increase being associated with excessive peristaltic 

 activity. There can be no reasonable doubt, however, that a portion of the 

 increase is due both to glandular activity and to the breaking down of the 

 absorbed products of digestion. 



The volumes of O absorbed and of CO, produced rise with an increase of 

 body temperature. This fact has been illustrated by the experiments of 

 Pfluger and Colasanti on guinea-pigs, in which they found that the quantity 

 of O absorbed at a body temperature of 37.1° was 948.17 cubic centimeters; 

 at 38.5°, 1137.3 cubic centimeters; at 39.7°, 1242.6 cubic centimeters, per 

 kilo per hour. Similar results have been obtained by other investigators in 

 experiments both upon the human subject and upon the lower animals under 

 the pathological conditions of fever. A fall of body temperature is accom- 

 panied by a decrease in the intensity of respiration, unless the fall is accom- 

 panied by muscular excitement, such as shivering. Speck 2 lias seen shiver- 

 ing cause the consumption of O to rise from 302 to 496 cubic centimeters, 

 and the exhalation of CCX, from 287 to 439 cubic centimeters. The primary 

 and fundamental effect of lowering the body temperature is to diminish respi- 

 ratory activity, but this may be more than compensated for by involuntary 

 or voluntary excitement of the muscles (p. 433; see also Tissue-respiration). 



The effects of cricrinil fem/icrature upon warm- and cold-blooded animals 

 are different: Molesohotl found that frogs produced three times more C0 2 at 

 38.7° than at 6°, while in warm-blooded animals the opposite is the case — that 

 is, three times more CO a is formed at the lower temperature. The frog's tem- 

 perature rises and falls with changes in the temperature of the surroundings, 

 while that of warm-blooded animals remains at a fairly constant standard; 

 he 'ee the respiratory intensity in the frog increases with the rise of external 

 temperature, while in warm-blooded animals it decreases, owing to diminished 

 heat-production. But in warm-blooded animals the alterations in respiratory 

 activity caused by changes of external temperature are not always in inverse 

 relation. Thus, Voit has shown, as a resull of studies in man, that the exhala- 

 1 Lor. tit. ' Deutsche* Archiv /. klin, Med., 1889, Bd. 33, S. 375, 424. 



