288 BIOLOGICAL PROBLEMS 



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fort and to lower physical and mental efficiency; that 

 such symptoms set in when the body temperature 

 rises above 99 F. ; that continuous work is impossible 

 with a W.B.T. of 78 F. ; and that 2000 cubic feet of 

 air per head per hour at about 60 F. are generally 

 required to regulate suitably the physical state of the 

 atmosphere of occupied rooms. Although the amount 

 of respiratory CO 2 in the air (within a likely degree of 

 "overcrowding") does not matter, it remains a useful 

 index to bad air conditions; for although a low figure 

 of respiratory CO 2 does not, per se, guarantee a satis- 

 factory atmosphere, the harmful physical changes in- 

 crease pretty much part passu with the respiratory 

 CO 2 . If, then, we allow an adult 2000 cubic feet of 

 fresh air per hour, this will keep down the CO 2 respira- 

 tory impurity to 0.036 per cent, and it will keep the 

 temperature and humidity within hygienic limits. 

 Even in the winter months an individual can readily 

 train himself to tolerate an air movement that will 

 change the air in the room two and a half times per 

 hour, and so 800 cubic feet of space will suffice for 

 one adult; but if he can secure 1000 cubic feet, the air 

 need be changed only twice in every hour. 



How do foul air conditions operate in favouring 

 actual disease? Let us first consider communicable 

 disease. It is certain that the depressing effect of foul 

 air reduces our resistance to many forms of infection, 

 and so increases the susceptible portion of the com- 

 munity. Catarrh is the cause of much inefficiency. 

 It is fostered by foul air conditions, and the subse- 

 quent chilling to which they expose us; and, like 

 influenza, measles, diphtheria, spotted fever, con- 

 sumption, &c., it is often spread to susceptible per- 

 sons in the immediate vicinity by infection organisms, 

 in particles of moisture discharged from a sufferer 

 in the acts of coughing, sneezing, and forcible speak- 



