THE NERVO-VASCULAR SUPPLY OF THE LUNGS. 479 



which solely subserve the process through which venous blood 

 is converted into arterial blood and are therefore distributed 

 to the lobules. 



If we now inquire into the nature of the nervous mech- 

 anism through which their functions are governed, we are led 

 in the light of our own views to an interpretation similar 

 to that found to satisfy the needs of other organs. The com- 

 parison of a pulmonary lobule to a racemose gland is some- 

 times met with in text-books; examination of a lobule soon 

 shows that its structures sufficiently correspond to that of the 

 glandular organs we have studied to enable us by analogy to 

 ascertain the nature of its relations with nerve-terminals. 

 Miller, we have seen, refers to the "exceedingly fine capillary 

 net-work shrunken into the epithelium of the air-sacs so that 

 between the epithelium and the capillary there is only the 

 extremely delicate basement membrane" Again, he refers to 

 the subdivision of the pulmonary artery "which divides quite 

 abruptly, a branch going to each infundibulum"; from the 

 latter "small arterioles arise which supply the alveoli/ 7 while 

 these on reaching the air-sac are said to culminate in "the rich 

 system of capillaries to which they give rise." The italicized 

 words but repeat what we have emphasized elsewhere as the 

 integral constituents of all glands. As will be shown later on, 

 however, the alveoli present histological features which further 

 emphasize their identity as parts of an autonomous system. 



There is but one feature wanting to complete the mechan- 

 ism common to glandular structures: i.e., the delicate nerve- 

 terminals distributed to the lobular cells. "The final ter- 

 mination of the nerve-filaments within the pulmonary tissue 

 is still undetermined," says Piersol; but under precisely similar 

 morphological conditions elsewhere in the organism terminal 

 fibrils have been clearly discerned. That the pulmonary lobule 

 should represent an exception to the rule is hardly probable: 

 a view indirectly sustained by the prevailing belief that the 

 mucous surfaces contain "secretory fibers." We have seen 

 that Frangois-Franck, Cavazzani, Henriquez, Rose Bradford, 

 and Dean have ascertained that vasomotor phenomena pre- 

 vailed in the lungs under stimulation. The implied presence 

 of this class of nerves completes the list of structures that 



