RESPIRATION. 



349 



those of Vieron.lt. He found that the quan- 

 tity of carbonic acid gas evolved from the 

 body at the freezing point, was double of that 

 at an elevated temperature, in the two mice 

 and guinea-pi^, and a little more in the canary 

 and pigeon. There can, therefore, be no doubt 

 that more carbonic acid gas is evolved from 

 the body in a cold, than in a warm tem- 

 perature. 



Effect of the seasons. Dr. W. F. Edwards* 

 ascertained, by several well-devised experi- 

 ments, that birds placed under exactly the 

 same circumstances, and with the surrounding 

 air of the same temperature, consumed more 

 oxygen in winter than in summer, and this 

 appears to be connected with that change in 

 the constitution of the warm-blooded animals 

 in the colder regions of the earth, by which 

 they are enabled to generate more caloric in 

 winter than in summer. 



Barometric pressure. Legallois found that 

 when warm-blooded animals breathed air in a 

 vessel under an atmospheric pressure reduced 

 to 30 centimetres (Jl'811 English inches), the 

 quantity of oxygen gas consumed was dimi- 

 nished.-}- Prout, on the other hand, informs 

 us, that, in every instance in his experiments, 

 any remarkable increase in the percentage of 

 carbonic acid in the expired air was accom- 

 panied by a sinking barometer. J Vierordt 

 tested the effects of a range of the barometric 

 scale between 330"' (29-309 English inches) 

 and 340'" (30'197 English inches), and has 

 thrown the results into a tabular form. The 

 measure of the expired air was calculated 

 under the ordinary pressure of 336'" (29-841 

 English inches). He found that a rise of 

 5"'-67, (the mean between the experiments at 

 the lower and those at the higher pressures,) 

 produced the following effects : 



It increased the pulsations in one minute 1 '3 



respirations 0'74 



expired air (cubic in.) 35'746 



As, however, the percentage of the carbonic 

 acid in the expired air was greater at the 

 lower than at the higher pressures, in the 



Centigrade scale, but we believe that it was the 

 latter. 



* De Flnfluence des Agens Physiques sur la Me, 

 chapitre vi. 



f Anuales de Chimie et de Physique, torn. iv. 

 p. 113. 1817. 



J Thomson's Annals of Philosophy, vol. iv. p. 335. 



proportion of 4'450 to 4' 141, the difference 

 between the absolute quantity of that gas in 

 the expired air at the higher exceeds so little 

 that at the lower pressures, that it may be 

 reckoned as nil.* 



Age, sex, and constitution of body. The 

 quantity of carbonic acid evolved from the 

 body is not only influenced by the ingesta and 

 the varying conditions of the surrounding 

 media, but also by the age, sex, and constitu- 

 tion of the body. The only important re- 

 searches into the effects which these last con- 

 ditions of the body have upon the evolution 

 of the carbonic acid, are those of Andral and 

 Gavarret f, and Scharling J ; and though they 

 are far from having exhausted the subject, 

 they possess the merit of having been care- 

 fully and accuratelv conducted, and of being 

 carried on in the right direction. Andral and 

 Gavarret availed themselves in their experi- 

 ments of the apparatus suggested by Dumas 

 and Boussingault. Part of this apparatus 

 consists of a mask, which can be fitted air- 

 tight to the face, and having a tube on each 

 side, on a level with the commissures of the 

 lips, provided with valves permitting the ex- 

 ternal air to pass in, but preventing its pas- 

 sage outwards. In front of the mouth there 

 is a large aperture for conducting outwards 

 the expired air; and to this a tube can be at- 

 tached for conducting it into the receivers 

 and other parts of the apparatus prepared for 

 ascertaining the quantity of carbonic acid gas. 

 A person can breathe through this apparatus 

 without constraint ; and the experiments were 

 all performed between one and two o'clock 

 P.M., each lasting from eight to thirteen mi- 

 nutes, and the individuals experimented upon 

 were placed, as far as possible, under the 

 same conditions with regard to food, muscular 

 exertion, and state of the mind. They ex- 

 perimented upon sixty-two individuals of dif- 

 ferent ages, and of both sexes. They restricted 

 their valuation of the quantity of carbonic 



* Dr. Hutchinson (Medico-Chirurgical Transac- 

 tions of London, vol. xxix. p. 228) has given 

 some experiments upon the effects of an increased 

 barometric pressure upon the frequency of the re- 

 spiratory movements. These were made upon six 

 persons before and after descending a mine, 1488 

 feet deep, where the barometric pressure was 1-54 

 inch more than at the level of the sea. As there was 

 a difference of 10 degrees in the temperature at the 

 top and bottom of the mine, this ought to be taken 

 into account in judging of the results. The pulse 

 was increased at the bottom of the mine on an aver- 

 age 1-3 per minute, and the respirations 2-4 per mi- 

 nute. The accounts given by travellers of the effects 

 upon their respiration in elevated regions are so 

 discordant that we can deduce no very satisfactory 

 conclusions from them. 



f Aunales de Chim. et de Phys. torn. viii. p. 129. 

 1843. 



J Anualen der Cliemie und Pharmacie, band xlv. 

 S. 214. 1843, translated in Annales de Chim. et de 

 Phys. torn. viii. p. 478. 1843. In Scharling's ex- 

 periments, as in those of Andral and Gavarret, the 

 absolute quantity and not the percentage of car- 

 bonic acid gas in the expired air was determined. 

 In Scharling's first experiments, the carbonic acid 

 gas given off at the external surface of the body 

 was mixed with that given off by the lungs. 



