passed toward the finger. Make sure that the fistula is a complete one, by feeling the probe touch the finger. There may not be an internal opening; if not, see how near the probe comes to the surface of the bowel. [Illustration: Fig. 22—Pratt's Speculum.] If a doubt still exists as to the completeness of the track, one of a variety of specula (Figs. 22, 23, 24) may be introduced into the rectum, and the outer orifice of the sinus injected with either milk or a solution of iodine, when if there be an internal opening the appearance of the colored fluid within the bowel will set the question at rest. If the inner opening be not discovered by these methods, the case must be looked upon as one of external rectal fistula. [Illustration: Fig. 23—O'Neil's Speculum.] [Illustration: Fig. 24—Kelsey's Rectal Retractor.] According to Ball,[44] in cases where the probe passes away from the rectum and is directed along the anal fascia to the upper portion of the ischio-rectal fossa, or where the entire substance of the rectal wall separates the finger and the probe, the case is one either of external rectal sinus, or of fistula originating in the superior pelvi-rectal space. In such cases, Mr. Ball states, "we must go farther and try and find the cause, such as diseased bone, etc.; and in the female a vaginal examination may show us a uterine or ovarian origin. Where there are numerous external openings it is necessary to carefully probe all of them, so as to determine whether they are all connected, and the direction which they take. The upper limit of the separation of the mucous membrane should also be made out, and search should be made for the presence of more than one internal orifice, if such is likely to be present." The presence of incomplete internal rectal fistula is more difficult to determine than the other varieties of this lesion which have just been considered. It is the most painful form, but, fortunately, it is of infrequent occurrence. Its orifice may be located anywhere in the rectum, but is generally found between the internal and external sphincters. According to Allingham,[45] the circumference of this opening is often as large as an English threepenny piece, its edges being sometimes indurated, at other times undermined. The feces, when liquid, pass into the sinus and create great suffering—a burning pain often lasting all day after the bowels have acted.