50 APPENDIX, 



instantaneously io the lung's through the action of the respired au>, but that it appeals 

 be secerted to a considerable extent, from the blood in the respiratory organs. 



As to the quantity of this gas which is formed during respiration, different physiolo- 

 gists have estimated it differently. Godwin considered that for every 100 cubic inches 

 of atmosphere respired, there were given off 10 or 11 of carbonic acid. Menzies, from 

 experimentsmade with much accuracy, found the quantity of carbonic acid to be about 

 5 in the 100. Dr. Murray considered it to vary from 6 to 6.5. Sir H. Davy from 3.95 

 to 4.5. Messrs. Allan and Pepys from 5.5 to 9.5, They estimated the mean at about 8. 

 Dr. Prout found it to be about 3.45. Dr. Fyi'e about 8.5. The discrepancies which are 

 remarkable in these results of the experiments performed by these physiologists doubt- 

 less arose, in a great measure, from the different proportions of this gas, produced by 

 different individuals according to the state and developement of the lungs, and accord- 

 ing to the particular circumstances of the individual at the time of the experiment. 



The influence which the state of the individual exerts upon the function was first 

 shown by the experiments of Dr. Prout and Dr. Fyfe. They proved that the carbonic 

 acid gas formed during respiration is liable to be very materially affected in its quantity 

 in the same individual, by various circumstances. It was formed in a minimum quanti- 

 ty during the night ; and the maximum quantity, which was generally produced about 

 noon, exceeded the minimum about one-fifth of the whole. The passions of the mind 

 were found to have a great influence over its production ; the depressing passions di- 

 minishing its quantity, and those of an opposite nature the reverse ; exercise, when mo- 

 derate, appeared to increase in some measure the quantity, but fatigue diminished it. 

 The greatest decrease experienced was from the use of alcohol and vinous liquors, es- 

 pecially when they were taken upon an empty stomach. In short, whatever diminished 

 the powers of life, as lo\v diet, mercurial irritation, &c. appeared from the experiments 

 of Dr. Prout and Dr. Fyfe to have the effect of diminishing the quantity of the carbonic 

 acid. 



Dr. Crawford found the quantity of this gas was much diminished when respiration 

 \yas performed in a high temperature ; and Lavoisier and Saguin confirmed his obser- 

 vation. Nearly similar results to theirs were obtained from some experiments which 

 we performed in 1815 ; and from the data thus obtained we endeavoured* to account 

 for several of the most important diseases to which the inhabitants of warm countries 

 are liable. Similar experiments were afterwards performed in an intertropical cli- 

 mate, where we found the diminution of the quantity of carbonic acid to be considera- 

 bly greater than that which our experiments, in an artificial temperature of equal ele- 

 vation had furnished. This seems to be accounted for by the depressing influence upon 

 the nervous system which the atmosphere, loaded with moisture and malaria, may be 

 reasonably expected to produce. We also attribute a share of this discrepancy to the 

 increased function of the skin, which evidently co-operates, in hot climates with the 

 the lungs, and performs a subordinate respiratory function. We shall not pursue this 

 particular topic farther at this place, as we propose considering it more at length on a 

 Future occasion. 



Reverting to the question whether the carbonic acid is formed ivit/iin the vessels, or 

 without them ; we must remark, that the evidence on the subject is very contradictory. 

 The experiments of Dr. Edwards, already referred to, show that the former process ex- 

 ists, at least to some extent ; and it is farther supported by the fact established by Ber- 

 zelius, that blood, especially its colouring part, not only absorbs oxygen very quickly, 

 but it also retains some part' of the carbonic acid thereby produced ; but whether or no 

 this absorption will take place through the parietes of the capillaries, is the point at is- 

 sue. The evidence for the absorption of oxygen through the capillary parietes is, how- 

 ever, nearly on a par with that for the excretion of the carbon ; if the vessels will per- 

 mit the transmission of the one, they may allow the transit of the other. 



Those who contend for the passage of the carbon from the vessels, and who, conse- 

 quently consider thai the carbonic acid is formed externally as respects the vessels, 

 support their opinon by the experiments of Mr. Ellis, who first promulgated the doc- 

 trine. His experiments, were, however, performed out of the body, and under cir- 

 cumstances which entirely excluded the operation of the vital influence of the lungs and 

 of the system generally. 



The must conclusive experiments in favour of this opinion are those performed by 

 Messrs. Magendie and Orfila. They found that phosphorus, dissolved in oil, and inject- 

 ed into the jugular vein of a dog, was expelled by the mouth and nostrils in the form 



* These views were contained in a Latin Theses written at Edinburgh. 



