70 HISTOLOG V OF NUTRIENT FL UIDS. 



vessel wall is quite common, tuberculous patches appearing 

 and disintegrating the wall, producing hemorrhage if in an 

 artery, or in a vein admitting bacilli and products of degen- 

 eration into the blood. 



2. Sclerosis is a local thickening of the inner coat of an 

 artery, generally in patches or plaques. The white or yellow- 

 ish patches are called atheromatous patches and the eroded 

 spots atheromatous ulcers. The whole process is known as 

 atheroma. There is often a calcification of the affected spots. 

 Atheroma may result from chronic endarteritis or degenera- 

 tion. It produces serious obstruction to the circulation and 

 may end in obliterating the artery. 



3. Aneurism is local dilatation of an artery involving all its 

 coats. The inner and outer middle coats may atrophy, leav- 

 ing the outer as the only covering. It is generally caused by 

 atheroma or sclerosis, although an embolism may also cause a 

 sac, as in some vessels in the brain, or there may be a hernial 

 protrusion of the inner coats through a weak place in the 

 sheath. 



4. Arterial hcematoma is the term given to a mass of coagu- 

 lated blood from a ruptured aneurism. The rent may be 

 closed by cohering leucocytes, and the part formed into a 

 bulging sac, the interior of which communicates with the 

 lumen of the vessel, while the exterior is formed by fibrin and 

 the clots resulting from the hemorrhage. Such a sac is called 



false aneurism, distinguished from the true by the coats of the 

 vessel forming no part of its wall. If the blood from the rup- 

 ture strips the outer from the middle coat it is termed a dis- 

 secting aneurism. 



5. Capillary dilatation, when general, is termed capillary 

 ectasis ; when more local, capillary aneurism. The first is the 

 result of chronic congestion; the latter may be congenital, as 

 in naevus, or the result of morbid change in the tissue around 

 the capillaries. 



6. Venous dilatations are known as plilebectases, or varices, 

 and usually occur from mechanical obstruction. Venous sac- 

 culations or sinuses on the hemorrhoidal veins surrounding 

 the anus form hemorrhoids, and dilatation of the veins of the 



