DISEASES OF THE AKTEEIES. 411 



on animals have confirmed its possibility; and the frequency 

 with which identity of structure has been detected between 

 the embolus and other substances yet undetached at distant 

 parts of the stream, together with the fact that in some cases 

 it has been possible to trace the intruder to the spot which it 

 has just left, by comparison of surfaces, as you detect a 

 burglar by the nails in his boots, has given additional 

 weight to the evidence; while the absence of any appearance 

 of pre-existing disease around the occluded vessel, and the 

 suddenness with which the effect is produced, are circum- 

 stances which attend no other kind of arterial obstruction. 

 But the solid substance in the blood may be of any size, from 

 one sufficient to obstruct the pulmonary artery to that which 

 would pass even a small capillary; therefore, among emboli 

 we may reckon not only fibrinous clots from the heart, 

 polypi, as they were once called, but fragments of decaying 

 or suppurating tissue, and the elements of tubercle and can- 

 cer. Indeed, our author asserts embolism to be the one 

 cause of secondary deposits in these diseases." 



The late Mr Barlow addressed the following letter to Dr 

 Gairdner, shortly before his death : 



" 1, PILRIG STREET, Dec. 12, 1855. 



" MY DEAR SIR, I have recently met with a few instances 

 in which arteries of considerable size have been almost 

 entirely plugged up with fibrinous clots, firmly adherent to 

 their walls. In these cases during life, there was sometimes 

 visible but unexplained atrophy of certain muscles, in regions 

 specially supplied by such vessels; and sometimes when a 

 main trunk, such as the aorta posterior became thus plugged, 

 there was palsy of the hind parts (of course I speak of the 

 horse.) At first I fancied these things to possess no material 

 interest, and did not preserve the vessels. jSowever, this 

 day week, a pony, greatly disabled behind, but not com- 

 pletely paralytic, was brought for dissection. I found a 



