The French maritime hospitals reported in 1890 about 1.5 per cent of all cases were treated for tapeworm infections and the United States hospital service during the Civil War recorded only 0.012 per cent treated for tapeworm, a record that is certainly much lower than the true degree of infection in this country.
The bladder worm, or larval stage in the life history of the tapeworm, is found encysted in the flesh of a great variety of hosts. It gains entrance to the final host when the flesh containing the cysts is ingested. When set free by digestion the bladder-worm everts the head and neck region which were formed in inverted fashion on the inside of the hollow spherical or oval larva. The bladder itself is digested but the chain of proglottids grows out from the neck.
The beef tapeworm (Tanis soginata), also celled the unarmed tapeworm of man because the scolex is devoid of hooklets, inhabits the small intestine of man but has not been found in any other host. The bladder-worm (Cysti cercus bovis) occurs in the muscles and viscera of cattle. As is natural from the cosmopolitan distribution of both hosts this parasite occurs over the entire world but is more common in those regions where the habit prevails of eat ing beef underdone or rare. It is also increas ing in frequency as shown by the statistics of the French maritime hospitals which report 33 cases among 130,927 or 02 per 1,000 during 1861-65 ; and 1886-90, 2,253 were infected among 152,352, or nearly 75 times as many as at the earlier date. Attention has already been called to the head of this tapeworm which with the neck is highly muscular and variable in form. The reproductive organs are not visible except as faint strands of tissue in full grown pro glottids; they have the form represented in Fig. 2. The numerous small round masses are the testes which communicate by vessels with the common sexual pore at the side. Generally speaking these pores alternate for the shell comes from the so-called yolk gland or vitellarium. At this stage of develop ment the uterus appears as a median sausage shaped receptacle. When the eggs accumulate it is increased in size so greatly that numerous lateral branches are formed extending almost to the margin of the proglottid, giving the aspect shown in Fig. 3.
The segments of this tapeworm when evacuated are little more than sacs covering the much branched uterus which is crowded with eggs. They possess considerable power of independent movement and are frequently found at some distance from the point of de posit. The eggs have several coverings which serve to protect them even after the disintegra tion of the proglottid. Distributed by chance an egg reaches the stomach of an ox with the food or drink of the animal. Under the stimulus of the gastric juice the membranes are ruptured and spherical six-hooked larva escape. It bores its way through the wall of the alimen tary canal and comes to rest in the connective tissue. When it reaches a suitable location it develops by growth and the accumulation of a considerable amount of fluid in the centre to a bladder-worm. A thickening of the wall of the bladder produces an ingrowth in which is formed in reverse the head of the future tape worm. Growth is slow and in six months the
worm measures only six millimeters or less in diameter. If the flesh containing the bladder worm is consumed by man while the parasite is still living the head of the bladder-worm is everted and it attaches itself to the wall of the intestine and begins to grow into a mature speci men. This period of growth requires no more than 9 or 10 weeks for the production of mature proglottids. Since a moderate tem perature is unfavorable to the bladder-worm well-cooked meat cannot possibly carry the in fection. Exposure to cold storage conditions for three weeks is also adequate to destroy all the bladder-worms contained in a piece of beef.
The pork tapeworm (Tcenia solium) is known as the armed tapeworm of man because of the crown of minute booklets which is found on the anterior face of the scolex. Like the preceding species it is confined in the adult condition to the small intestine of man. Its bladder worm (Cysticercus cetitslom) occurs in the muscles and viscera ordinarily of the pig from whence the common name of the parasite. It also occurs in the dog, cat, rat, ape and rarely, also, in man. While the dis tribution of both parasite and bladder-worm is as broad as that of the previous species yet there are certain parts of the world where it is entirely wanting, i.e., among those people who do not eat the flesh of the pig. The species is common in European countries where pork is consumed in the smoked but uncooked condition and is very uncommon in the United States because of the general practice of eating pork well done. The parasite is somewhat more slender than the beef tapeworm. The terminal proglottids (Fig. 3) show that the branches of the uterus are less numerous and heavier than those of that species, but to dis tinguish between them is not always easy. A positive determination can readily be made when the scolex is obtained because of the presence of hooks in a double circle in which they alternate regularly in size. In general the pork tapeworm is less muscular and more transparent. Its life history is similar except that the eggs find opportunity for hatching and development in the pig rather than in cattle. The species is more dangerous than the preced ing form because of the fact that the bladder worm may develop in the human host. Appar ently the brain and the eye are the points in which they have been more frequently observed and the cerebral cysticerci are most dangerous because they produce naturally conditions similar to brain tumors and are not infre quently the cause of sudden death. There are no special symptoms connected with their presence and usually it is not possible to dis tinguish between them and tumors of different origin. The bladder-worm displays in some situations a marked longevity as the same in dividual has been followed by means of the opthalmoscope for 20 years in the human eye. Because of the campaign against the use of pork except when well cooked this parasite has grown much rarer within recent years.