The tendency to the occurrence of abscess and fistula in phthisical patients has long been recognized, and has given rise to some doubts as to the propriety of resorting to operative measures in such cases. This point will be considered in the chapter on Treatment. According to Messrs. Cooper and Edwards,[43] about five per cent. of phthisical subjects also suffer from fistula, and about twelve per cent. of fistulous patients are the subjects of tuberculosis. VARIETIES.—For all practical purposes we may divide fistulæ into the following four forms: (1) the _complete_ fistula, in which there are two openings, one in the rectum and one on the skin more or less remote from the anus (Fig. 15); (2) the _incomplete internal_ fistula, in which there is a communication with the cavity of the rectum by means of an opening in the mucous membrane, but none with the external surface of the body (Fig. 16); (3) the _incomplete external_ fistula, in which there is an external opening through the skin, but no communication with the bowel (Fig. 17); and (4) the _complex_ fistula, in which there are many sinuses and numerous external openings (Figs. 18 and 19). Some of these tracks run outward; some extend up the bowel beneath the mucous membrane; whilst others travel round the bowel and open in the other buttock, giving rise to the so-called _horseshoe_ fistula. The second and third varieties named are often spoken of as _blind_ fistulæ. [Illustration: Fig. 15—Complete Fistula traversed by Probe (Esmarch).] [Illustration: Fig. 16—Internal Incomplete Fistula (Esmarch).] [Illustration: Fig. 17—External Incomplete Fistula (Esmarch).] [Illustrations] FISTULÆ WITH DOUBLE TRACKS (MOLLIÉRE). Fig. 18—A, B, deep submuscular track resulting from an ischio-rectal abscess; A, I, submucous track running up and down the bowel. Fig. 19—D, E, subtegumentary and submucous fistula with internal and external opening; D, F, deep submuscular track, having same internal but separate external opening. ----- Footnote 33: _Op. cit._, p. 152. Footnote 34: _Op. cit._, p. 13. Footnote 35: _Op. cit._, p. 13. Footnote 36: _Op. cit._, p. 66. Footnote 37: _Op. cit._, p. 67. Footnote 38: _Op. cit._, p. 13. Footnote 39: Keating's "Cyclopædia of the Diseases of Children," vol. iii, p. 341. Footnote 40: Allingham, _op. cit._, p. 14. Footnote 41: Article on Diseases of the Rectum, by Henry Smith, Esq., revised by John H. Packard, M.D., in Holmes' "System of Surgery" (Packard, editor of American edition), vol. ii, pp. 643-644. Footnote 42: "Diseases of the Rectum and Anus," second edition, London, 1892, p. 126. Footnote 43: _Op. cit._, p. 126. CHAPTER II. SYMPTOMATOLOGY—PHYSICAL EXPLORATION—DIAGNOSIS—PROGNOSIS.