INFLUENCE OF THE MOISTURE OF THE AIR. 347 



of carbonic acid. I have made several experiments in reference to 

 this subject on wood-pigeons, green-finches, and rabbits. The 

 weight of carbonic acid excreted in moist air greatly exceeds 

 that eliminated in a dry atmosphere ; thus, for instance, 1000 

 grammes 5 weight of male wood-pigeons yielded in one hour in the 

 morning in a dry air 10*438 grammes of carbonic acid at 0, 6 055 

 grammes at 24, and 4*69 grammes at 37; in a moist atmosphere 

 they yielded 6'769 grammes at 23, and 7*76 grammes at 37. 



In the same way 1000 grammes' weight of green-finches yielded 

 in the course of one hour in the afternoon in dry air 7*260 

 grammes at 0, 5*679 grammes at 17*5, and 3*220 grammes at 

 37*5. In moist air they yielded 5*351 grammes at 17*5, and 

 6*851 grammes at 37'5. Lastly, 1000 grammes' weight of rabbits 

 exhaled in one hour before noon 0*451 of a gramme of carbonic 

 acid in dry air at a temperature of 37*5, and as much as 0*677 of 

 a gramme in a moist atmosphere at the same temperature. 



Few as these investigations are, they yet clearly demonstrate 

 the importance of this influence on respiration, which we have 

 frequently had opportunities of observing at the bed-side, more 

 especially in the case of pulmonary diseases. It is only when we 

 proceed to inquire into the causal connection existing between the 

 excretion of carbonic acid which is here observed, and the degree 

 of moisture of the inspired air, that we are compelled to admit our 

 insufficient knowledge of this subject. 



The influence exerted by the moisture of the air on the respira- 

 tory movements is not a question of mere conjecture, since it 

 admits of direct observation. The respirations of animals are more 

 frequent in a moist warm atmosphere than in a dry one ; but this 

 result depends very much upon the change to which the animals 

 are subjected at the beginning of the experiment ; but when the 

 frequency of the respiration is observed, 3, 6', or 10 hours after the 

 commencement of the experiment, it is always found to be more 

 considerable than in a dry atmosphere. It appears, however, from 

 some experiments made by Buchheim in my laboratory, that the 

 moisture of the air even more decidedly influences the depth of the 

 inspirations. But although the augmentation in the expired car- 

 bonic acid, when breathing in a moist air, may be partially ex- 

 plained by the alteration in the respiratory movements to which we 

 have already referred, the influence of moisture, like that of the 

 temperature, probably also acts in some other way. Our knowledge 

 of these relations does not as yet enable us to prove that the 

 aqueous vapour exerts any direct influence on the excretion of 

 carbonic acid from the blood. I have repeatedly made an obser- 



