1879.] The Function of Respiration at Various Altitudes. 229 



falling off in the prodnction of carbonic acid, or lessens comlmstion in 

 the animal body. 2. That increase of light, especially of violet and 

 blue light (the most actinic rays), either causes, or greatly predis- 

 poses to the formation of an increase of carbonic acid, thereby pro- 

 moting animal combustion. 



These results do not, it will be observed, apply to the united action 

 of heat and light, but to the influence of heat and light considered 

 separately. They are, I fear, calculated to give us but little assistance 

 towards a knowledge of the influence of tropical climates on the 

 phenomena of combustion in progress in the healthy human body. 



The only direct experiments and observations on that subject, with 

 which I am acquainted, are those of Dr. Rattray, alluded to in my 

 paper. He finds that the body loses weight in passing from a cold 

 into a tropical climate, and regains it on its returning under a colder 

 latitude ; and, moreover, that in tropical countries the temperature of 

 the body has a distinct tendency to rise slightly above its normal con- 

 dition in temperate zones. The increased waste of tissue, and the 

 rise of temperature of the body under a tropical sun, even should it 

 only be trifling, appear to me to show a tendency to increased com- 

 bustion in the body in a tropical climate ; and the marked excess of 

 carbonic acid I found to be exhaled under tbe sun of Teneriffe in July 

 and August, over that given out near the Lake of Geneva and in the 

 Alps, is quite in keeping with Dr. Rattray's observations. 



What is the cause of this increased combustion and waste of tissue 

 under a tropical climate ? Is it the excess of the sun's heat, is it the 

 increase of the sun's light, or is it a combined action of both ? After 

 what has been reported in this note, it must be concluded that the 

 answer is difficult to give, and we must await further experiment to 

 be able to explain this very interesting and important phenomenon. 



So far my two communications to the Royal Society, on the in- 

 fluence of altitude upon respiration, have been strictly limited to brief 

 summaries. I have not yet given the history of what has been done 

 on that subject, otherwise I would have had many important physio- 

 logical contributions to cite ; these I shall propose to consider on 

 another occasion. 



vol. xxrx. 



R 



