526 RESPIRATION 



presently give way to infrequent convulsive efforts and these in turn 

 to slow and shallow respirations and finally to mere spasmodic twitches. 

 At this time, the pupils are markedly dilated, the reflexes are extinct, 

 the integument is cyanosed, and the extremities stiffened. The urine 

 and feces are voided generally before the heart has ceased to beat. 

 The blood pressure rises during the early stage of dyspnea, but falls 

 gradually as soon as the respiratory and cardiac depression has set in. 

 Inasmuch as the heart usually continues to beat for several minutes 

 after the cessation of respiration, it is still possible at this time to 

 resuscitate the animal. 



Ventilation. — The problem of ventilation is essentially a physio- 

 logical one and has to do primarily with the chemical properties of the 

 respiratory air, and secondarily with its temperature and its content 

 in water vapor. Consequently, ventilation provides not only for a 

 continuous supply of pure air in place of that vitiated with the products 

 of metabolism, but also of air possessing a stimulating temperature and 

 a content in aqueous vaipor in keeping with the physiological require- 

 ments of the body. An undue emphasis, however, should not be placed 

 upon any one of these factors at the expense of the others. 



Ventilation does not purpose to bring outdoor conditions indoors, 

 but simply to make indoor conditions fit for indoor life. As far as the 

 composition of the air is concerned, we know that an adult person in- 

 spires about 500 c.c. of air seventeen times in a minute and that his 

 output of CO2 at rest amounts to 17 liters, or to 0.68 cubic feet in an 

 hour. During gentle exertion this value rises to 0.9 and during actual 

 work to 1.8 cubic feet per hour. Assuming then that the normal 

 amount of CO2 is 0.03 per cent., the percentage of this gas in 1000 

 cubic feet (28,000 liters) of air will be increased to about 0.1 percent, 

 in the course of an hour. Obviously, therefore, the amount of fresh 

 air required per hour to keep the CO2 at 0.06 per cent., is 0.03 : 0.6 :: 

 100 : X or a; = 2000 cubic feet. If the normal amount of CO2 is reckoned 

 at 0.04 per cent., 3000 cubic feet must actually be provided for, but 

 naturally, this amount may be supplied in three lots of 1000 cubic 

 feet each. Furthermore, an allowance must be made for the weight 

 of the person, because a woman of 120 pounds exhales only 0.6 cubic 

 feet of CO2 in an hour and a child of 80 pounds only 0.4 cubic feet. It 

 is also essential to take account of the type of work to be performed by 

 these individuals. 



In regard to O2, little need be said, because even in the worst ven- 

 tilated spaces the air seldom approaches a basis of 15 volumes per cent., 

 at which respiration can still go on undisturbedly. Hence, we are 

 chiefly concerned at this time with the CO2 content of the respired air, 

 but its value should serve merely as a working unit to indicate the 

 degree of vitiation of the air, because even in the worst ventilated rooms 

 it is rarely present in amounts sufficient to exert a pernicious influence. 

 Ordinary increases are endured for some time without discomfort, 

 provided that the temperature and the humidity of the air remain 



