l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 60 



centration of C0 2 which rules the respiratory center, and to such 

 purpose as to keep the concentration both in the lungs and in the 

 blood uniform. (J. S. Haldane.) The only result from breathing 

 such a slight excess of C0 2 as 0.5 per cent (slight to the physiolo- 

 gists, but regarded as enormous by the hygienist) is an unnoticeable 

 increase in the ventilation of the lungs. The increased ventilation 

 is exactly adjusted so as to keep the concentration of C0 2 in the 

 lungs always at the normal 5 to 6 per cent of an atmosphere. The 

 very same thing happens when we take gentle exercise and produce 

 more C0 2 in our bodies ; the pulmonary ventilation is slightly in- 

 creased, and thus the concentration of C0 2 in the blood and lungs is 

 kept the same. 



We turn to the evidence of former researchers. Leblanc 1 found 

 that an animal could survive exposure to an atmosphere containing 

 30 per cent of carbon dioxide, provided the percentage of oxygen 

 was 70 per cent, and recover quickly from the depression produced 

 by this mixture. So, too, Regnault and Reiset 2 found that an animal 

 could survive exposure to an atmosphere containing a relatively high 

 concentration of C0 2 so long as sufficient oxygen was supplied. 



Pettenkofer J demonstrated clearly that the symptoms produced in 

 crowded ventilated places were due neither to excess of C0 2 nor 

 deficiency of 2 . He found that 1 per cent of C0 2 could be breathed 

 for hours with no discomfort. Pettenkofer did not regard the 

 impure air of dwellings as directly capable of originating specific 

 disease, or as a poison in the ordinary sense of the term, but con- 

 cluded that the capability of withstanding the influence of disease- 

 producing agencies was diminished in those who continually breathed 

 such air. He laid down the doctrine accepted by sanitarians, that 

 the percentage of C0 2 is a guide to the other deleterious properties 

 of the atmosphere. 



It is manifest, however, in regard to the heat, moisture, and move- 

 ment of a confined atmosphere, that the C0 2 percentage may give 

 no indication, and fails wholly as an adequate test. 



R. A. Smith 4 enclosed men in a chamber and found that the pulse 

 frequently fell from 73 to 57, while the frequency of respiration rose 

 from 15 to 24, in an atmosphere in which the C0 2 increased 





1 Ann. de Chim. et Phys. Paris, 1842, (3), v, 223. 



2 Ann. de Chim. et Phys. Paris, 1849, (3), xxvi, p. 299. 



8 Ann. de Chem. u. Pharm. Leipzig u. Heidelberg, 1862-3, 2. Suppl. Bd. p. 

 1-52. 



' Air and Rain. London. 1872. 



