284 



THE VITAL FUNCTIONS. 



their nutritious juices, or a very imperfect one ; 

 but no sooner do we arrive at the examination of 

 animals possessing an enlarged system of blood 

 vessels, than we find nature abandoning the system 

 of tracheae, and employing more simple means of 

 effecting the aeration of the blood. Advantage is 

 taken of the facility afforded by the blood-vessels 

 of transmitting the blood to particular organs, 

 where it may conveniently receive the influence of 

 the air. Thus Scorpions are provided on each side 



of the thorax, with four pulmonary cavities, seen at 

 L, on the left side of Fig. 374, into each of which 



gen, nitrogen, and carbonic acid gases, in any proportion, in a 

 membranous bladder, which was then immersed in aerated water, 

 found that there is a reciprocal transit of the gases ; until at length 

 pure atmospheric air remains in the cavity of the bladder. 



