SYSTEMATIC ANALYSIS OF APPARATUS. 105 



vance of need so can the water, to a more limited extent; 

 but air can only be stored for a moment's time, and with 

 each returning circuit of the blood the life-giving influ- 

 ences of the air must be breathed upon it, and its poison- 

 ous burden drawn out, or the pulse fails to perform its 

 now useless task, and animation will be suspended. 



378. THE RESULTS OF PRODUCING HEAT and the like 

 results, which are so great in quantity as to require that 

 all the Blood at each circuit should be sent through an 

 organ adapted to eliminate them, are gases dissolved 

 in the Blood, or substances that very easily become 

 gases by contact with pure air, and by its influence are 

 in either case easily withdrawn from the blood; therefore, 



379. THE RESPIRATORY ORGANS ARE REQUIRED, in 

 order that the Blood and Air may be freely and rapidly 

 brought within influence of each other. 



380. TWO THINGS ARE THEREFORE TO BE PROVIDED 



FOR : one, the mode of bringing the Blood to the Air, 

 and the other, the mode of bringing the Air to the Blood. 



381. THE METHOD OF BRINGING THE BLOOD TO THE 

 AIR has been described in a previous section. A Heart 

 exists, ready to pour its contents into arterial tubes 

 leading to a network of capillaries, through the sides of 

 which air, if present, can act upon and be acted upon by 

 the Blood, when it is ready to return to the other Heart, 

 and be sent on its way. 



382. IT ONLY REMAINS TO DEVISE some way by 

 which Air shall be brought to act freely through the 

 sides of the capillaries. 



383. IF A SMALL SAC OR CELL BE CONSTRUCTED with 



exceedingly delicate sides, composed in part of the net- 

 work of capillaries, with a tube through which Air can 

 be drawn into the cell, the material of which has a cer- 

 tain amount of elasticity, it will be complete, and a mi- 

 nute lung will be formed. 



378. What form have ? 379. Why ? 380. What ? 381. What is 

 2. What-? 383. What ? 

 5* 



