RESPIRATION. 199 



He asserts, 1st, That the subdivisions of the 

 bronchia? occur more and more thickly, the 

 twigs propc rtionally decreasing in diameter 

 and length, and that each ultimate twig ends 

 in a close bulbous extremity, or cell, com- 

 municating with other bulbous extremities 

 only in an indirect manner, by means of 

 the twigs which end in them. Malpighi had 

 described them as round, and mere dilata- 

 tions in the course as well as at the ends of the bronchial twigs. k 

 2d, That, as Malpighi proved, and contrary to the subsequent 

 opinion of Helvetius and others, these ramifications and cells 

 have no connection with the surrounding common cellular mem- 

 brane. 3d, That they consist of, 1. mucous membrane, behind 

 which lies, 2. a coat of elastic white fibres, their existence being 

 visible as far as the canals can be traced, and the regular discharge 

 of any fluid injected into the bronchise after death proving the 

 existence of elasticity in the bronchial ramifications; 3. a coat 

 of muscular fibres, transverse relatively to the course of the canals, 

 and visible by the aid of a magnifier as far as the size of the canals 

 will allow them to be traced. He conceives the muscularity of 

 the twigs and cells to be shown also from the necessity for its ex- 

 istence in them no less than in the large trunks and trachea, 

 where it is visible ; from their evident contraction in the experi- 

 ments of Varnier, who irritated them by the injection of stimulating 

 liquids and gases, and by mechanically stimulating the surface of 

 the lungs 1 ; and from the circumstance of the lungs shrinking much 

 more if an opening is made in the thorax of a living than of a dead 

 animal, in the latter of which it can shrink from elasticity only. 

 4th, That the ramifications of the bronchial and pulmonary arteries 

 freely anastomose both in the air-passages and on the surface of 

 the lungs, and that the bronchial arteries run chiefly direct to the 

 pulmonary veins. 5th, That the air-passages and blood-vessels of 

 the lungs are most abundantly supplied with nerves from the par 

 vagum, whose conjunctions with the sympathetic take place ex- 

 ternally to the lungs. m 



" The common membrane investing the lungs is the chief seat 

 of a remarkable network of lymphatic vessels n which run to nu- 



k Ejiist. de Pulmon. 1. p. 133. 



I Memoires de la Societt Royale de Mtdecine. 1779. p. 394. gqq. 



m Some other conclusions are drawn, but unimportant or unsatisfactory. 



II " Mascagni, His tor, vasor. lymphaticor. tab. xx." 



