366 RESPIRATION. 



material. These particles thus penetrate the lung substance, 

 from which they can never be removed. They may find 

 their way into the lymphatic vessels, but become fixed in the 

 lymphatic glands, in which the quantity is always propor- 

 tionate to that which exists in the lungs. It has been shown 

 that the particles introduced under the skin in tattooing may 

 also be taken up by the lymphatics, but are arrested and 

 fixed in the glands. 1 



There is no ground for the hypothesis that the carbona- 

 ceous matter of the lungs and bronchial glands is deposited 

 as a residue of combustion of the hydrocarbons, in the process 

 of respiration. 



Movements of Respiration. 



In man and the warm-blooded animals generally, the 

 lungs attain their greatest degree of development, the sur- 

 face which is exposed 'to the atmosphere is relatively great- 

 est, and it is in these organs that nearly all of the process of 

 interchange of gases takes place. In all animals of this class, 

 inspiration takes place as a consequence of enlargement of 

 the thoracic cavity, and the entrance of a quantity of air 

 through the respiratory passages corresponding to the in- 

 creased capacity of the lungs. In the mammalia, the chest is 

 enlarged by the action of muscles; and in ordinary respi- 

 ration, inspiration is an active process, while expiration is 

 comparatively passive. In many birds, the chest is com- 

 pressed by muscular action in expiration, and inspiration is 

 effected in a measure by elastic ligaments. In both classes, 

 the air is drawn into the chest to supply the space produced 

 by its enlargement. In some of the lower orders of animals 

 which have no ribs or sternum, or in which the thorax is 

 immovable and there exists no division between its cavity 

 and the abdomen, the air is forced into the lungs by an act 

 like deglutition. In these animals (frogs, lizards, turtles, 



1 The results of the investigations of Robin are to be found in the Chimic 

 Anatomigue, by RODIN and VERDEIL, tome iii., p. 605 et scq. 



