Attempts have been made to estimate the time taken in the formation of a calculus by allowing a ring for each feed and successive deposit therefrom (Fürstenberg, Colin). Thus a calculus of 14 pounds with 720 layers, it was estimated could be formed in one year at two feeds per day. More definite evidence was found in the case of Pastore in which a coin with the mint mark of 1847 was found as the nucleus of a calculus the size of the fist in 1848. _Lesions._ Formed in the most spacious parts of the colon and cæcum, calculi usually rest there for a length of time without visible injury, and it is only when they are moved onward and get arrested at a narrow part of the gut (pelvic flexure, floating colon, rectum) that they cause appreciable trouble. Yet it is claimed that by their weight they drag upon the yielding walls of the bowel, causing dilatation and attenuation, weakening the peristalsis and predisposing to rupture. The compression of the vessels also tends to anæmia and atrophy. In the case of rough crystalline calculi the mucosa is subjected to attrition, irritation, and inflammation. The more serious and urgent trouble is that of obstruction of the narrower portions of the colon and rectum, which may be absolute and persistent, leading to rupture and death or a fatal inflammation on the one hand, or may end in recovery on the other, in connection with a displacement onward or backward of the calculus as the result of peristalsis or anti-peristalsis. _Symptoms._ These are intermittent colics, each reaching a climax and followed by a sudden recovery as the calculus is displaced into a more spacious part of the colon. A significant feature is the complete obstruction, fæces being passed for a short time at first and then suddenly and absolutely stopped. Coincident with this are tympany, violent colics, straining, rolling, sitting on the haunches, perspirations, anxious countenance, and all the symptoms of obstruction. _Diagnosis_ is never quite certain unless the practitioner with his oiled hand in the rectum can detect a hard stony mass obstructing the pelvic flexure of the double colon with a tense elastic distended bowel immediately in front of it, or a similar hard obstruction of the terminal part of the floating colon with a similar distension in front of it. The pelvic flexure may usually be felt below and to the right at the entrance to the pelvis, and the floating colon above, under the right, or more commonly the left kidney. Calculi in the more spacious parts of the double colon or in the cæcum are inaccessible to manipulation. The feed (bran, ground feed) will be suggestive, as will the occupation of the proprietor (miller, baker).