244 LECTURE X. 



which are no longer to be followed with the naked eye, 

 and in them it usually extends as far down as a point of 

 division and somewhat beyond. This mass constantly 

 presents a finely granular appearance, and does not con- 

 sist of the coarse debris that we find in the veins, but of 

 a very fine, yet at the same time dense, granular matter ; 

 chemically, it possesses the extremely convenient quality 

 for examination of being remarkably resistant to the ordi- 

 nary tests, and thus readily distinguished from other mat- 

 ters. This is capillary embolia properly so called, one of 

 the most important forms of metastasis, which frequently 

 gives rise to minute deposits in the kidney, the' spleen, 

 and the substance of the heart itself ; in certain cases 

 occasions sudden occlusions in the vessels of the eye or 

 brain, and according to circumstancs produces metastatic 

 deposits or sudden functional disturbances (amaurosis, 

 apoplexy). Here too one can clearly convince oneself 

 that in recent cases the wall of the vessel is quite unal- 

 tered at the seat of the affection ; nay here indeed the 

 doctrine of phlebitis would no longer suffice, since these 

 are not vessels which possess vasa vasorum, and concern- 

 ing which it might be assumed that a secretion proceeded 

 from the wall inwards. In these cases it is impossible to 

 regard the occluding mass in any other light than as one 

 primarily existing in the vessel, and in no wise depend- 

 ent upon the condition of its wall. 



Perhaps this description has convinced you, gentlemen, 

 that two essential errors have existed in the doctrine of 

 pyaemia ; the one, that people thought they had found 

 pus-corpuscles in the blood, when only colourless blood- 

 corpuscles were really present ; the second, that they 

 thought they had found pus in vessels in which nothing 

 more than the products of the softening of fibrine existed. 

 Yet we have ascertained that this last class of cases cer- 

 tainly furnishes the most important source of genuine 



