382 THE SOLIDS. 



cells, through the medium of a beautiful and elaborate system 

 of plexuses, each air cell being furnished with its own sepa- 

 rate plexus. 



The manner in which the vessels, either arteries or veins, 

 are distributed throughout efich lobule is as follows : first, 

 large branches, after having reached the lobule through the 

 interlobular spaces, extend over an area of several cells (See 

 Plate XL VII. Jig. 2) ; from these, secondly, a number of 

 smaller vessels proceed, which run in the spaces between 

 the cells, forming loops arpund them (See Plate XL VII. 

 Jig. 3); third and last, from these intercellular vessels the 

 capillaries constituting the plexuses are given off. (See 

 Plate XLIX. Jig. 3.) This distribution of the vessels is 

 especially evident on the pleural surface of the lung. 



From the preceding description it does not appear that 

 the capillary plexus belonging to each air cell is compounded 

 of both venous and arterial capillaries, but that in most cases 

 it consists entirely of capillaries derived exclusively either 

 from a vein or an artery. 



It is thus evident that an air cell with its investing plexus 

 of capillaries contains all the essential constituents of an en- 

 tire lung, and therefore that each air cell may be regarded as 

 a lung in miniature. 



It is well known that it is frequently a matter of great 

 moment, in a medico legal respect, to discriminate between a 

 lung naturally inflated and one artificially so : the test pro- 

 posed and ordinarily employed and relied upon, seems to me 

 to be unworthy of full confidence. I allude to the hydrostatic 

 test: it is stated that, by firm pressure, all the air contained 

 in a portion of lung artificially inflated may be expressed, so 

 that it will sink in water ; but that this cannot be done in 

 the case of a lung naturally inflated ; a portion of air will 

 always remain unexpressed sufficient to keep it afloat. I sec 

 no good reason for this constant difference, since it is perfectly 

 certain that a lung may be most completely and entirely in- 

 jected with air or fluid, far more completely, I should be in- 

 clined to say, than occurs with air naturally inspired, except 

 perhaps during a forced inspiration. Notwithstanding the 



