428 TEXT-BOOK OF PHYSIOLOGY 



increase due to the oxidation of food materials after absorption. It was 

 found that in a fasting man a dose of sodium sulphate increased the absorp- 

 tion of oxygen as much as 17 per cent, and the discharge of CO 2 24 per cent. 

 (Lowy). It is difficult to determine how much of the increase after a meal 

 is therefore due to food oxidation and how much to functional activity 

 of the canal itself. The consumption of nitrogenized meals, however, has 

 a greater effect than non-nitrogenized meals. 



Temperature. A rise in temperature of the surrounding air has as 

 an effect diminution in the amounts of oxygen consumed and carbon 

 dioxid discharged. A fall in temperature has the opposite effect. Thus 

 a cat at a temperature of 3.2C. consumed during a period of six hours 

 21.39 grams of oxygen and discharged 22 grams of carbon dioxid, while at 

 a temperature of 29.6C. the corresponding amounts for the same period of 

 time were for oxygen 13.9 grams and for carbon dioxid 13.12 grams. Lavoi- 

 sier and Sequin, having reference only to the oxygen, found that a man 

 at a temperature of i5C. consumed 38.31 grams of oxygen, while at a tem- 

 perature of 32.8C. the corresponding amount was but 35 grams. Similar 

 results have been obtained by other observers with different animals. The 

 explanation of these facts is to be found in the increased activity of all 

 physiologic mechanisms coincident with a fall, and in the decreased activity, 

 coincident with a rise in temperature. The lower temperatures act as a 

 stimulus to the peripheral terminations of the nerve system, bringing about 

 reflexly increased activity of the body at large. The muscles especially are 

 not only reflexly but volitionally excited to greater activity. This leads 

 naturally to an increase in the consumption of oxygen and in the production 

 of carbon dioxid and in the evolution of heat. 



In cold-blooded animals the respiratory exchange is influenced in a 

 manner the reverse of that observed in warm-blooded animals. With a 

 rise of external temperature and a corresponding rise of body-temperature 

 the discharge of carbon dioxid steadily increases. Thus a frog in an atmos- 

 phere at oC. with a body- temperature of iC. discharged per kilogram 

 per hour 4.31 c.c. of carbon dioxid; in an atmosphere of 35C. with a body- 

 temperature of 34C. there was discharged 325 c.c. per kilo per hour. 

 Intermediate temperatures were attended by corresponding increases in 

 the amounts of CO 2 discharged. The reason for this difference in the two 

 classes of animals is probably to be found in the cold-blooded animals, in 

 the want, of,a self-adjusting heat-regulating mechanism. 



Age. In early youth, as a result partly of the more pronounced activity 

 of the nutritive energies and partly of a cutaneous surface relatively greater, 

 as compared with the mass of the body, than in adult life, the absorption of 

 oxygen and the discharge of carbon dioxid are greater both absolutely and 

 relatively. Thus, in a boy of nine and a half years with a weight of 22 

 kilograms it was found that in twenty-four hours there was a discharge of 

 carbon dioxid amounting to 488 grams, or 0.92 gram per kilo per hour, and 

 in man with a weight of 65.5 kilograms there was a discharge of 804.72 

 grams, or 0.51 gram per kilo per hour. 



THE NERVE MECHANISM OF RESPIRATION 



The nerve mechanism by which the respiratory muscles are excited to 

 and coordinated in activity is extremely complex and involves the action of 



