CLIMATE 901 



rate increased by 39 from 67 to 106 as the atmospheric temperature 

 rose from 74 to 110 F. and the relative humidity from 58 to 90 per 

 cent. The effect of humid heat upon the blood pressure does not appear 

 to be uniform. Young, Breinl, Harris and Osborne found the systolic 

 pressure rose at times and fell slightly at others. The New York State 

 Commission on Ventilation observed that excessively high temperatures 

 and high humidities were accompanied by an elevation of both systolic 

 and diastolic pressures. The reactions of the vasomotor mechanism, as 

 judged by Crampton's scale of vasotone, indicate that a distinct vascular 

 benefit follows the exposure of the body to a cool dry air. 



The influences of atmospheric heat and humidity on the respiration are 

 varied in character. A moderate degree of both seems to be without effect 

 on the rate of respiration ; but more extreme rises cause a quickening of 

 the breathing, which is probably accompanied by more shallow respira- 

 tions. Young and collaborators found that the alveolar air in inhabitants 

 of tropical Queensland showed a lower carbon dioxid content than the 

 European average. A slight seasonal influence has been noticed by Boy- 

 cott and Haldane, in which a higher alveolar carbon dioxid partial pressure 

 was found in cold and a lower in warm months. These changes were not 

 attributed to variations in the body temperature but to the contact of the 

 body with cold or warm air. A marked increase in relative humidity also 

 lowers the alveolar carbon dioxid content. 



The influence of high temperature and high humidity on the capacity 

 for physical work, the amount of blood per kilogram of body weight, and 

 the concentration of sugar in the blood is pronounced. Lee and Scott ex- 

 posed cats for periods of six hours to an abundance of moving air, varying 

 in respect to temperature and humidity, using a "low" condition in which 

 the average temperature was 69 F. and the humidity 52 per cent; an 

 "intermediate" condition in which the average temperature was 75 F. 

 and the humidity 70 per cent; and a "high" condition in which the 

 temperature was 91 F. and the humidity 90 per cent. Muscles taken 

 from these animals and stimulated to exhaustion showed that the average 

 duration of the working periods and average total amounts of work per- 

 formed decreased progressively from the low, through the intermediate, 

 to the high condition. The amount of blood taken from the cats was less 

 after exposures to the high than the low condition. The concentration of 

 sugar in the blood also decreased progressively in the three groups from 

 the low to the high condition. The evidence indicates that the distaste 

 for physical labor which is felt on a hot and humid day has a deeper basis 

 than mere inclination ; that it is founded upon physiological factors. 



Atmospheric conditions likewise influence the nasal mucosa. Miller 

 and Cocks demonstrated that exposure of the body to heat increased the 

 swelling, redness and secretion of the nasal mucosa ; and that the effects 

 were more marked when the humidity of the air was high. High tern- 



