Page:The American Cyclopædia (1879) Volume VI.djvu/677

ENTOZOA 665 erally they are swallowed by the hog, whose filthy and omnivorous habits need only be con- sidered to show how readily it may become in- fected. In either case the egg shell is destroyed by the process of digestion, and the embryo, a minute globular vesicle, armed in front with three pairs of sharp spines, begins its active migrations. It sets out on its travels by boring into the blood or lymph vessels of the stomach or intestine, and is borne along by their cur- rents till it reaches the capillaries, where it re- news its activity and bores its way out of the circulatory system into any organ to which chance has carried it. There can be no doubt about this fact, for Leuckart has discovered the embryo several times in the vena portae. It is possible that the embryos may in some cases lose their booklets in the vessels, and thus, being unable to proceed further, become encysted in the capillaries. Having reached thus a proper situation for higher develop- ment, it becomes surrounded by a new forma- tion or cyst resembling the structure of the organ it may inhabit. If it happens to pene- trate any serous cavity, this cyst is not formed, but otherwise the development is the same. This process goes on rapidly, so that in a week or two the cyst may be recognized by the naked eye. The spines or booklets now drop off, the primary vesicle goes on absorbing nu- triment, and by the second or fourth week a protuberance grows out from its inter- nal surface, which soon takes the form of the head of the future tasnia. Upon this springs up a FIG. 2.- Development of a Cyst, double Circle _of 1. Animal in cyst. 2. Animal Small hairs, which with head developed. 3. Head insix Weeksbecome magnified the complete double coronet of hooks. The neck now begins to extend, but the head still remains enclosed in the bladder, till the whole animal is set free. It may continue to live in this encysted stage till it dies of old age, unless set free by nature or art ; and this undoubtedly is the fate of the largest portion of these immature creatures. If seated in the muscles, this encysted stage of tapeworm is seldom injurious to man ; but if it take up its dwelling place in the brain or eye, which is not unfrequently the case, results most serious follow. In the hog the case is different, for many eggs being devoured at once, the em- bryos invade nearly every organ of the body, and produce the disease known as measles. We have still to consider the last and highest stage of development in the life of a tasnia, viz. : the conversion of these cysts or measles into the mature intestinal worm. When one of these cysts is accidentally swallowed by man, the little pea-like vesicle bursts, and the head of the worm protruding fastens itself to the intestinal walls by its hook- lets. From this head bud out one after an- other numerous joints, which finally make up the mature worm. It may be easily under- stood how these small white cysts gain en- trance into the stomach of man, for measly pork is often sold in markets, and although FIG. 8. Hooklets of a Cyst, magnified. FIG. 4. Cyst found in Swine. thorough cooking and curing destroy the larvso, still the cysts may adhere to the knife, and be thus transferred to vegetables, butter, cheese, and the like, which are eaten uncooked. It may often be the case too that pork is so slightly measly, that the butcher does not know the disease is present. There can be no ques- tion about the identity of these two forms, the tcenid solium in man and the cysticercus cellu- losce or measles in swine ; for not only are their heads anatomically the same, but it had for a long time been noticed that where measles in pork were abundant, there tasnia was of most frequent occurrence, and that where the use of this flesh was forbidden among nations or sects, there tapeworm was scarcely ever found. All of this led to the belief, especially after the experiments performed in regard to the tasnias and cystic worms of the lower animals, that the measles in meat were the cause of tape- worm in man. To settle this point Ktichen- meister fed a condemned criminal three days before his execution on raw measly pork, and on examination after death the young tape- worms were found attached to the walls of the intestine. One point, however, remained to be proved, viz. : that the eggs of the tapeworm produce the measles in swine. For this pur- pose experiments were undertaken by the Saxon government under the direction of Kii- chenrneister and other scientific men of Ger- many. Young and healthy pigs were kept confined separately, and to them were given the eggs of tapeworms. At various intervals they were killed, and the encysted forms were found in myriads throughout the body. These ex- periments have been often repeated with the same success. To recapitulate : The tapeworm of the human intestine discharges millions of eggs, a single one of which need only reach maturity to produce millions more ; therefore it is evident that the vast majority of these eggs perish undeveloped. These eggs must be de- voured by some other host to reach their second or encysted stage. This stage is known as mea- sles in swine. Measles being eaten by man in turn produce the tapeworm. These two forms never produce each other in the same individual,.