Thrombosis and Embolism. 493 



plete and anaemia and gangrene are liable to occur unless the blood 

 supply is partially maintained by anastomotic vessels. When the 

 embolism affects a number of smaller arteries or capillaries in a 

 vascular organ like the lungs, the blood filters in from the adja. 

 cent capillaries, in which circulation is still carried on, and this 

 passes through the softened and ruptured capillary walls so that 

 the tissue is charged with globules and constitutes a black infarc- 

 tion. In the lung this usually affects one or several lobulettes, 

 forming a pear-shaped mass corresponding to the distribution of 

 the obstructed vessel. The cut surface is black, compact and 

 granular. The lymph thrown out around it forms an organized 

 fibrous sac, and the enclosed sequestrum undergoes a slow necro- 

 biosis, blanching and liquefaction into a pus-like fluid which is 

 removed by absorption. Such results are met with in the paren- 

 chymatous organs (lungs, liver, spleen, kidneys, etc.) and less 

 frequently in the limbs. The symptoms will correspond to the 

 particular organ invaded. 



In the fore or hind limbs the result is usually less radical. The 

 vessels below the obstructed trunk are connected more or less 

 freely by anastomosing branches, so that the circulation in the 

 tissues below, though somewhat restricted, remains active enough 

 to sustain a fair measure of nutrition. Apart from the suffering, 

 attendant on the preliminary inflammation, the morbid phenomena 

 are largely confined to the absence of pulsation in the lower part 

 of the limb and the inability of the muscles to sustain active con- 

 traction. 



Chronic Embolism of the External Iliac or Femoral Ar- 

 tery. In this condition the pulsations in the digital arteries are 

 imperceptible, if it has been of long standing there may be obvious 

 atrophy of the muscles of the thigh, but when standing quietly or 

 walking, there is usually no lameness. In continuous rapid walk- 

 ing and, above all, in the trot, however, he soon begins to halt on 

 the affected limb, and this rapidly increases, the joints bending 

 under his weight, the toe dragging and the animal threatening to 

 drop altogether. If stopped and allowed to rest for ten or fifteen 

 minutes he gradually recovers and may be led quietly back to his 

 stable without a sign of lameness. But if again trotted fifty or 

 one hundred paces the lameness develops anew and disappears in 

 the same way when left at rest. The circulation in the muscles 



