Some medical authorities of the sixteenth century were disposed to regard the calculus produced by the human subject as superior in medicinal efficacy to the far-famed bezoar. One of their arguments was that as man was the highest type of organized being a human product must exceed in value one from an animal source; then again, his food was of the best, superior in quality to that taken by the animals furnishing the bezoars. For every theory a proof can be found if one is on the lookout for it, and therefore we need not be surprised if the virtues of calculi or gravel were also supported by evidence. In 1624 or 1625 the Dutch city of Leyden was visited by the plague, and to the great regret of the physicians there was no supply of bezoars on hand. Hereupon they were driven to make use of human gravel, and found to their astonishment that this was an even more excellent sudorific than the bezoar itself.[444] [Illustration: Calculi taken from the bladder of Pope Pius V. From Mercati’s “Metallotheca Vaticana.” Romæ, 1719. ] Although there is no direct relation between bezoars and the hair-balls sometimes found in the stomach or intestines of human beings, there is some slight analogy, as the animal bezoar concretions seem to have been formed about a nucleus consisting of some indigestible material that has been swallowed by an animal. From the report of hospital surgeons, it appears that these hair-balls, which result from a long-continued habit of swallowing hair, are almost exclusively found in the bodies of women, generally of very young girls. The large size which they sometimes attain is very surprising; in several instances they have so filled up the stomach that they are moulded by it into its exact shape. Although when a hair-ball has reached this size, and indeed long before, the most alarming symptoms set in, frequently recurrent vomiting being the most characteristic, we cannot but wonder how it is possible for _any_ food to enter and pass through the stomach under such conditions, the only explanation being the great power of dilation this organ possesses. Its disposition to patiently tolerate foreign bodies where it cannot expel them, renders it often a poor guide in a diagnosis based upon the patient’s personal experience. These hair-balls accumulate and lodge not only in the stomach but also in the intestines, and in either case the eventual result is almost certain to be fatal unless the obstacle is removed by operation. Very occasionally only does nature react sufficiently to expel the impediment without surgical aid. Of course all treatment is vain unless the morbid habit of hair-swallowing can be overcome. This does not seem to be an accompaniment of a distinctly diseased mental condition, although that is sometimes coincident, but must assuredly result from some derangement or abnormality of the nervous centres, inducing a morbid and unnatural craving.[445] [Illustration: