234 EXTENT OF THE RESPIRATORY EXCHANGE OF GASES. 



and energetic persons of the same size and weight. The consumption 

 of oxygen and the excretion of carbon dioxid are in inverse proportion 

 to the extent of body surface. In this connection the respiratory 

 gaseous interchange pursues a course parallel with that of heat-pro- 

 duction. 



4. Diurnal and Nocturnal Variations. In general there is during 

 sleep a diminution in the excretion of carbon dioxid as compared with 

 the waking state (the proportion being 100 : 145, in the most extreme 

 case 100 : 169). This is proportional to the diminution of the general 

 metabolism resulting from the constant heat of the surroundings (the 

 bed), the darkness, the absence of muscular activity, and the abstinence 

 from food (see 5, 9, 6, 7). According to v. Pettenkofer and C. v. Voit 

 and others a slight accumulation of oxygen seems to take place during 

 sleep. After awaking in the morning the respirations become deeper 

 and more rapid, with at first an increase in the excretion of carbon 

 dioxid. In the course of the morning, however, the excretion diminishes 

 again, until the midday meal causes a fresh increase to the maximum. 

 A falling off takes place again in the afternoon, and finally an incon- 

 siderable increase is produced by the evening meal. 



During hibernation, in which, together with the taking of food, respiration is 

 entirely discontinued, and the interchange of gases is carried on only by diffusion 

 in the lungs and the cardio-pneumatic movements, the excretion of carbon dioxid 

 falls to yV> and the absorption of oxygen to V of the respective amounts during 

 the waking state. Therefore, much less carbon dioxid is given off than there is 

 oxygen absorbed, so that the body weight may even increase in consequence of 

 the excess of oxygen taken up. 



5. Influence of the Surrounding Temperature. The bodily tempera- 

 ture of cold-blooded animals is easily raised by an increase in the sur- 

 rounding temperature. Under such circumstances the animals give off 

 more carbon dioxid than in a cooler state. For example, a frog exposed 

 to a surrounding temperature of 39 C. excreted almost three times as 

 much carbon dioxid as when the temperature was 6 C. Warm-blooded 

 animals behave in a varying manner with changes in the surrounding 

 temperature, accordingly as the bodily temperature remains constant, 

 or is correspondingly raised or lowered. In the latter case, as in cold- 

 blooded animals, a considerable decrease occurs in the excretion of 

 carbon dioxid, when the body is cooled under the influence of cold 

 surroundings. Conversely, elevation of the bodily temperature (also in 

 the presence of fever) gives rise to increase in the excretion of carbon 

 dioxid. The behavior is exactly the reverse when the bodily tempera- 

 ture remains constant on exposure to varying surrounding temperature. 

 With increasing cold of the surrounding medium, the consequent reflex 

 stimulation causes an increase in the oxidation-processes of the body, 

 as well as in the number and depth of the respirations. As a result, 

 more oxygen is taken up and more carbon dioxid is given off. The 

 involuntary muscular movement that occurs when the body is cooled 

 has the most obvious influence on the increase in the gaseous inter- 

 change. The season of the year also has an influence on the interchange 

 of gases; in January a man consumed 32.2 grams of oxygen hourly, in 

 July only 31.8 grams. In animals the carbon-dioxid excretion was 

 found to be about one-third higher with a surrounding temperature 

 below 8 C. than with a temperature above 38 C. When the tempera- 

 ture of the air increases (without change in the bodily temperature), 



