454 THE CIRCULATORY SYSTEM. 



Periarteritis Nodosa. 



A few cases have been described in which many of the small arteries in the muscles 

 and in the viscera were beset with small white knobs projecting from the side or sur- 

 rounding the vessels. These circumscribed thickenings of the vessel wall are apt to 

 involve all the layers of the vessel, and may encroach upon the lumen. The thickened 

 portions are infiltrated with small spheroidal cells. Multiple aneurisms may develop 

 at the seat of the local thickening. 1 



THE CONDITIONS LEADING TO ARTERIO -SCLEROSIS. The lesions of 

 arterio-sclerosis often occur with gout, syphilis, chronic lead and alcohol 

 poisoning, overwork and overfeeding. They are usual in senility, and 

 predisposition to them may be inherited. They may be associated with 

 cardiac hypertrophy from valvular lesions or with chronic diffuse ne- 

 phritis or other conditions involving increased arterial tension. They 

 may occur locally in connection with tumors. 



While the mechanical conditions under which arterio-sclerosis devel- 

 ops are not very fully understood, the studies of Thoma have pointed 

 the way along which fruitful research may be confidently expected. 



In accordance with the results of Thoma's experiments one may re- 

 gard the primary lesions of arterio-sclerosis as a compensatory hyperpla- 

 sia of the intima. For example, if for any reason the wall of the artery 

 in a given region, as is the case in the circumscribed or nodular forms of 

 arterio-sclerosis, be weakened and yields to the blood pressure, it is at 

 this point that the new tissue forms in the intima and restores the lumen 

 to its natural calibre (see Figs. 247 and 253) with restitution of the rate 

 of blood flow. That this compensation is often incomplete or tempo- 

 rary, or that it brings with it other and often serious complications, does 

 not militate against this view of the significance of these blood-vessel le- 

 sions, and is only one of many examples of imperfect adaptation in path- 

 ological processes. 2 



CLASSIFICATION OF THE FORMS OF ARTERIO-SCLEROSIS. Various 

 classifications of the lesions of arterio-sclerosis have been made. Thoma 3 

 places in one class the primary and more limited nodular forms of fibrous- 

 tissue growth, especially in the larger vessels, which he regards as com- 

 pensatory in the way just indicated; in another the diffuse or secondary 

 form, which is attributable to an increased resistance to the flow of blood 

 in peripheral vessels, such as those of the kidney, a weakening of the 

 muscularis through degeneration, the consequent dilatation, and then 

 the compensating fibrous-tissue growth in the vessels at large. 



Councilman 4 has grouped the lesions into three forms: 1st, the nodu- 



1 Consult v. KaJMen, Ziegler's Beitrage z. path. Anat, etc., Bd. xv., p. 581. 1894, 

 also Graf, ibid., Bd. xix., p. 181, 1896. 



2 See reference to Welch, p. 127. 



3 Thoma, see Virch. Arch., Bd. xciii., p. 443; ibid., Bd. cxvi., p. 1; also Thoma's 

 "Text-Book of General Pathology," vol. i., Eng. trans.; also reference to Thoma's 

 works, Arch. f. Entwickl. Mech., Bd. xii., p. 352. 



4 For a resume of views based upon Thoma's studies see Councilman, Trans. Assn. 

 American Physicians, vol. vi., p. 179, 1891. 



