602 PHYSIOLOGY OF RESPIRATION. 



The Size of the Bronchial Tree arid the Ventilation of the 

 Lungs. Since the reserve supply of air in the lungs may amount to 

 2600 c.c., while the new air breathed in at each inspiration amounts 

 to only 500 c.c., it would seem at first that the alveolar air is not 

 very efficiently renewed by a quiet inspiration. The actual amount 

 of ventilation effected depends on the capacity of the bronchial 

 tree, sometimes known as the "dead space" of the lungs, since 

 the air filling this space is not useful in the respiratory processes. 

 According to observations founded partly on measurements of 

 casts of the tree and partly upon physiological determinations 

 made by breathing air poor in oxygen, it would seem that this 

 volume may be reckoned at 140 c.c.* At each inspiration, there- 

 fore, at least 360 c.c. of air penetrate into the alveoli, and if evenly 

 disseminated through the lungs add about -$ to the volume of 

 each alveolus. Once in the alveoli, diffusion must tend to spread 

 the tidal air rapidly, and that this occurs is shown by an interesting 

 experiment performed by Grehant. He breathed in 500 c.c. of 

 hydrogen instead of air and then examined the amounts of hy- 

 drogen breathed out in successive expirations. Only 170 c.c. 

 were recovered in the first expiration, 180 c.c. in the second, 41 in 

 the third, and 40 in the fourth. 



Artificial Respiration. In laboratory experiments artificial 

 respiration is employed frequently after the use of curare ; when it is 

 necessary to open the chest; after cessation of respirations from 

 overdoses of chloroform or ether, etc. The method used in almost 

 all cases is the reverse of the normal procedure, that is, the lungs 

 are expanded by positive pressure (pressure in excess of atmos- 

 pheric). A bellows or blast worked by hand or machinery is con- 

 nected with the trachea and the lungs are dilated by rhythmical 

 strokes. Provision is made for the escape of expired air by the use 

 of valves or by a side hole in the tracheal cannula. Numerous 

 forms of respiration pumps have been devised for this purpose. 



In cases of suspended respiration in human beings from drown- 

 ing, electrical shocks, pressure upon the medulla, etc., it is necessary 

 to use artificial respiration in order to restore normal breathing. 

 Bellows ordinarily cannot be used in such cases. Some method 

 must be employed to expand and contract the chest alternately, and 

 several different ways have been devised. The Marshall Hall 

 method consists in placing the subject face down and rolling the 

 body from this to a lateral position, making some pressure upon the 

 back while in the prone position. The Sylvester method, which is 

 frequently used, consists in raising the arms above the head and 

 then bringing them down against the sides of the chest so as to 

 compress the latter. The Howard method consists in simply com- 

 * See Loewy, " Archiv f. die gesammte Physiologic," 58, 416. 



