The hydatids of hogs are found in the substance of the fat and in the muscles. They are sometimes so numerous as to be almost contiguous. The disease, besides measles, is sometimes called lepra; and on this account it seems to have been forbidden to the Jews, among whom the lepra was an endemic disease. The hydatids of hogs are most commonly lodged under the tongue; and, from inspection of that part, the probability of their existence in the flesh may be ascertained.

It has been doubted whether the hydatid of the human body is really a living animal, since its head has not been observed, and no motion is perceivable in it. We, must however, reflect, that the human body is seldom dissected soon after death; and that hydatids, whose heads are not naturally observable, may, by the management already described, be compelled to exhibit them. The hydatid of man is apparently more simple than that of sheep, but its general similarity is so striking that the analogy may be safely transferred; and who shall limit the simplicity of structure consistent with animation ? The subject is yet in its infancy, and this must be our apology for the extent of the present article. There are eighteen species described, the more important of which we shall describe.

1. The globular hydatid is cylindrical, terminated by a globular, very large, vesicle, found on the liver, the spleen, and other viscera of man. It is the largest species yet discovered.

2. The visceral hydatid is globular. Its vesicle is large anteriorly, and pointed posteriorly; it is described and figured by Goeze, found in the liver, the uterus, and the hydropic sacs of the human race; and probably a more frequent cause of dropsy than pathologists have suspected. The vesicles are often lined with an opaque, pulpy coat, but are more usually transparent. It is said that they are frequently contained in each other. This, however, we believe is not true; but we have seen numerous hydatids contained in a sac compressed, without any containing fluid, and apparently without life. When in the ovaria, their most frequent residence, they sometimes appear to occasion a false pregnancy. Treutler has described and figured, in a separate treatise, a visceral hydatid, which, instead of a head, had a small tubercle not retractile. The author thinks, with some reason, that many distinct species have been confounded under this title.

3. The cellular hydatid is contained in a cartilaginous vesicle, which has two appendices on its posterior part. It is described and engraved by Werner in an excellent work on the vermes intestinales. It is found in the integuments of the muscles of the human race, and has been supposed to be the same species with that which infests hogs.

4. The hydatic hydatid has an elongated body, large anteriorly, with a small vesicle, and a sessile head. It is found in the livers of rats.

5. The vervecine hydatid has a large vesicle, with a short body, rough, with an imbricated appearance, and found in the peritonaeum of sheep..

6. The cerebral hydatid is furnished with retractile tubercles, but has no visible vesicle. It is the animal which causes vertigo in sheep; and, by some naturalists, has been supposed to occasion mania in man.

7. The hydatid of the hog is conical, inclosed in a double sac, the interior of which adheres by its base. It has lately been removed to another genus, under the name of finna. Werner and his editor, Fischer, represent little pedunculated globules in the room of the corona of fangs; but Bosc, from frequent examination, asserts that he has always found the latter in this animal.

Three species are found in the viscera of the hare; three in those of a sheep, one in the ox, and one in the dolphin, which are not accurately distinguished. The granulated hydatid figured in Goeze, found in the liver of a sheep, is separated by Rudolph to a different genus, echinocoqus.

We must add, that Treutler has published, at Leipsic, a dissertation on many intestinal worms found in the human body, among which he has described a new species of hydatid (taenia alba punctato), found in the plexus choroides of a man who died in an idiotic state. The individuals of this 'species, instead of being inclosed like those of the cerebral hydatid in a common sac, arc united by their base through the medium of a membrane. Their form is globular; the largest about half an inch, the smallest 1/12 in diameter; their colour grey, spotted with black, with six fangs on their heads.

The more important part of the work remains, viz. to point out the means of removing the diseases by destroying the animal which has produced them. But this part of the task naturalists have overlooked; and, in general; hydatids lie out of the course of the circulation, so that little expectation can be formed of the success of any medicine. Moiigeot may have given us some information on this subject; but the only hint we can collect from those who have quoted his work is, the injection of a solution of common salt into the uterus, when the hydatids are known to exist in that viscus, from some being occasionally discharged. The circumstance of sheep being relieved, when placed in salt marshes, may suggest the use of common salt; but we must recollect that, in this case, the animal is generally diseased from a known cause, and that in case of plants, the insects which accompany or cause the complaint may be removed by restoring the health and strength. If we apply this to the human body we shall discover an excess of saline nourishment itself a cause of disease; and the prudent physician, who would pursue the hint, will probably find it necessary to be cautious how far in pursuit of a remedy for one disease he may-produce a worse. There may be some reason to suspect, that, when alkalis have relieved dropsies, and more certainly when mercurials have had a similar effect, they may have destroyed these animals which are, we fear, often an unsuspected cause of this disease. One other remedy we would suggest, viz. the sulphurated ammonia. We know that sulphur penetrates very minutely into every vessel of the system: we know that sulphurated hydrogenous waters are useful in cases of taenia, and it is highly probable that this may prove a valuable remedy in diseases which arise from hydatids; that it has really proved such, where the cause was unknown. Whatever may be the result, we have, at least, reason to think that medicines of this kind will not injure the constitution which they are given to relieve.

See Tyson, Philosophical Transactions, vol. xvii. p. 506, et ejusdem Tentamen Act. Eruditorum Lipsiae, 1692, p. 435; Schroeder de Hydatidibus; Pallas Miscellanea Zoologica; Werner, Vermes Intestinales; Goeze, der Lingeweidewurmer Thicrischer Rorper; Mougeot, Essai Zoologiquc et Medicalc; Medical Communications, vol. i. p. 101.; London Medical Journal, vol. i. p. 125; vol. vi. p. 139.