The parasite, which at first appeared straight, soon assumes a bent form, then that of a figure “6,” then of a figure “3,” and preserves a latent vitality throughout the entire period of encystment. These cysts are of very small dimensions, invisible to the naked eye, and their discovery necessitates the use of the microscope. They are about ¹⁄₆₄th inch in length and ¹⁄₁₂₀th inch in width. Very frequently two or three cysts may be found arranged in line, presenting the appearance of beads on a string: more rarely two parasites may be found in one cyst; exceptionally, as many as six or seven. The appearance of “beads on a string” is due to the fact that the parasites follow the interfascicular capillaries. In animals which are kept for a long time and fattened the cyst walls undergo fatty infiltration. The change is commonest in pigs. In the same way calcareous infiltration sometimes occurs, but only when the parasites have lost their vitality. This calcareous degeneration consists in the deposit of carbonate and phosphate of lime in the walls of the cyst; it never begins before the seventh or eighth month after infestation, and is sometimes much longer delayed. No man or animal ever becomes infested except by the ingestion of meat or drink containing larval trichinæ. The pig and small rodents are most frequently attacked. Man contracts trichinosis by eating insufficiently cooked infected pork. The fact that small rodents, particularly rats, eat the bodies of their kind explains the persistence of trichinosis in certain regions. Pigs roaming at large, and thus liable to find and eat the dead bodies of such rodents, may contract trichinosis in this way or from eating ordure. For some weeks after the larvæ have penetrated the muscular tissues the animals show stiffness of the limbs, difficulty in moving, and in mastication, etc., but these troubles disappear in a short time. The above facts explain why trichinosis in the pig is almost unknown in France, Italy, and Spain. It is commoner in Germany and in certain States of Europe, such as Holland and Russia, although investigations had previously shown that in Paris about 7 per cent. of the sewer rats were sufferers from trichinosis and that in Germany the percentage rose as high as 15 to 20. In Chicago and Cincinnati, U.S.A., the proportion of rats suffering from trichinosis has been as high as 50 to 70 per cent., and as in some of the Northern States pigs were bred in complete freedom, it follows that at one time very large numbers of American pigs must have suffered from trichinosis. In consequence of sanitary precautions this proportion has since greatly diminished.