540 AN 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 CO 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 CO 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 l 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 an insignificant 

 portion of the increase is due both to glandular activity and to the oxidation 

 of the absorbed products of digestion. 



The volumes of O absorbed and of CO 2 produced rise with an increase of 

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

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

 of O absorbed at a bodily temperature of 37.1 was 948.17 grams; at 38.5, 

 1137.3 grams; at 39.7, 1242.6 grams. 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 bodily 

 temperature is accompanied by a decrease in the intensity of respiration, unless 

 the fall is accompanied by muscular excitement, such as shivering. Speck 2 

 has seen shivering cause the consumption of O to rise from 302 to 496 cubic 

 centimeters, and the exhalation of CO 2 from 287 to 439 cubic centimeters. 

 The primary and fundamental effect of lowering the bodily temperature is to 

 diminish respiratory activity, but this may be more than compensated for by 

 involuntary or voluntary excitement of the muscles (p. 541 ; see also Tissue- 

 respiration). 



The effects of external temperature upon warm- and cold-blooded animals 

 are different : Moleschott found that frogs produced three times more CO 2 at 

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

 is, three times more CO 2 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^ce 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, Yoit has shown, as a result of studies in man, that the exhala- 



1 Loc. cit. * Deuisches Archiv f. Uin. Med., 1889, vol.. 33, pp. 375, 424. 



