144 LECTURE VI. 



and were, nothing more than channelling! or excava- 

 tions in the parenchyma of organs, as well as whether 

 vessels could not be produced by the formation of new 

 tracks in communication with the old channels by the 

 forcing asunder of the neighboring parenchyma ; there 

 can, at the present time, be no longer any doubt as to 

 the vascular system's being everywhere continuously 

 closed by membranes. In these it is not possible to 

 descry any porosity. Even the minute pores, which 

 have recently been observed in different parts, have not. 

 up to the present time, met with their counterparts in 

 the capillary membrane, and when the porosity of this 

 membrane is spoken of, the expression can only be 

 admitted in a physical sense, as applying to invisible, 

 really molecular interstices. A, film of collodion is not 

 more homogeneous, nor more continuous, than the mem- 

 brane of a capillary. A series of possibilities, which 

 used to be admitted, as that, for example, the continuity 

 of the capillary membrane did not exist at certain points, 

 simply fall to the ground. A " transudation " or dia- 

 pedesis of the blood through the walls of vessels without 

 the occurrence of any rupture cannot for an instant be 

 admitted ; and although we cannot in every individual 

 case point out the exact site of the rupture, it is, not- 

 withstanding, quite inconceivable that the blood with its 

 corpuscles should be able to pass through the walls in 

 any other way than through a hole in them. This is 

 such a very natural deduction from ascertained histolo- 

 gical facts, that all discussion upon the point is impos- 

 sible. 



After the capillaries have pursued their course for a 

 time, small veins begin gradually to form out of them, 

 and generally run back in the neighbourhood of the arte- 

 ries (Fig. 45, v). In them the characteristic circular- 

 fibre coat of the arteries is in general wanting, or at least 



