274 



RESPIRATION. 



on the flat expansion of a cell-wall. But it 

 is quite an error to suppose that each cellule 

 has its own separate arterial ramusctile. 

 Professors Harting and S. Van tier Kolk's 

 injections place this point beyond doubt : 

 " quod ad divisionem ramorum arteriarum at- 

 tinet, animadvertenduin est, non alveolum 

 quemque singulum ramulum accipere, quum hoc 

 tantum valeat de infundibulis, ita ut lobulus, 

 infundibula continens, accipiat truncuin arte- 

 riae, ille truncus ad numerum infundibulorum 

 dividatur et iterum subdividatur." (Adriani). 

 From this description it results that the ca- 

 pillary lueb without an intervening trunk 

 stretches from cell to cell. One more im- 



Fig. 224. 



Injected preparation of a single arterial tieig and 

 the attendant vein, showing a single plane of capil- 

 laries overlying the air-cells. The pleural capil- 

 lary system is distinguished from that of the true 

 pulmonary tissue by the greater denseness of the 

 vascular web and greater minuteness of the meshes 

 in the latter situation. (After Kottiker.} 



portant fact remains to be stated with refer- 

 ence to the capillary plexus. It is noivherc 

 doubled upon itself, as it is in the lung of the 

 reptile. Every cell-wall and every partition 

 between the cells bears only a single layer of 

 vessels. The opposed sides of such a layer 

 must therefore bound two different cells, and 

 the current of blood by which it is traversed 

 must be subjected on both its flat sides to the 

 action of air contained in the cells. If this 

 plexus were double, only one side could re- 

 ceive the influence of the atmosphere. This 

 type is exemplified in the reptilian lung. All 

 other things being equal the respiration of 

 the mammal and man must be twice in 

 amount that of the reptile. But this anato- 

 mical fact has also an interesting pathological 

 bearing. When the capillary layer, or rather 

 the blood borne by it, is the seat of disease, 

 the products of that disease must be poured 

 into the two contiguous cells, between which 

 it is interposed, at the same time and in the 



same amount. This accounts for the rapidity 

 with which pneumonic infiltration occurs. 

 In the most injected preparation the diameter 

 of the capillary vessels of the rete mirabile 

 exceeds that of the meshes. This, however, 

 is not an exact expression of their propor- 

 tions in the living state. The diameter of a 

 single capillary, measured in the injected state 

 on the wall of an air-cell, does not exceed 

 TiW (Todd and Bowman.) The human red 

 blood corpuscle ranges, in the same drop of 

 blood, from 7 oVw to WOTJ f an mcn m <na ~ 

 meter, the average being from -g^Vo to -j ^Vo- 

 Then two red-corpuscles may traverse any 

 single capillary abreast ? When allowance is 

 made for the difference between the internal 

 and external diameters of the vessel, it will 

 appear very probable that in man and mam- 

 mals only a single row of red-corpuscles tra- 

 verse the pulmonary capillaries at a time. In 

 the lung of the reptile it is to be proved by 

 observation of the living circulation, that a 

 double row of corpuscles really does move 

 along the vessels. This fact must reduce the 

 amount of oxygenation which in a given time 

 a single corpuscle receives. 



The pulmonary Veins convey the blood, 

 arterialised in the plexus just described, to 

 the left auricle. The distribution of the pul- 

 monary veins differs strikingly from that of 

 the artery and bronchia. Each lobule has its 

 separate arterial and bronchial branch. This 

 regularity does not obtain with respect to the 

 veins. The pulmonary veins arise in the form 

 of minute radicles in the capillary plexus of the 

 air-ceils. Now although, as formerly stated, 

 the individual air-cells are not furnished with 

 a separate arteriole and venule, the extreme 

 branches of the pulmonary artery and the in- 

 cipient venules are separated in different parts 

 of the lung by areas of similar dimensions. 

 It follows, therefore, that the time during 

 which a globule of blood in different parts of 

 the lung is exposed to the agency of the air 

 is equal ; in other words, every drop of blood 

 which enters the lung is arterialised to the 

 same amount from the equality of the areas 

 of exposure over which it passes. It should 

 also be observed that as the capillary web is 

 spread over several cells, every particle of 

 blood in transit u from artery to vein traverses 

 the circumferences of several cells. This is a 

 beautiful provision for securing certainty to a 

 vital process. The minute venules unite to 

 form visible trunks, which course irregularly 

 over and between the cells and intercellular 

 passages. They observe a general diagonal 

 direction, the bronchia and artery occupying 

 with great constancy the geometrical axes of 

 the lobule. They emerge out of this lobular 

 space not at its apex, in company with the 

 air-tube and artery, but at every or any point 

 of its circumference. This is more obviously 

 the case as regards the lobular veins along the 

 surface of the lung. Those more centrally si- 

 tuated follow the bronchia more closely. This 

 explains why Reisseissen, Cruvcilhier, and 

 others have expressed very opposite opinions 

 upon this point. In the intralobular spaces the 



