The specific symptoms (such as the muscular pain) of trichiniasis may be due in part to mechanical damage of the muscle tissue, but it is also probable that they are partly due to toxic products exuded by the worms and partly to the introduction of alien protein material--the protein of the worm--into the tissues. Secondary bacterial infection is also a possibility, but there is little evidence to prove that this is an important factor in most cases of trichiniasis. The various stages observed in the progress of the disease are plainly connected with the different phases of the worm's development--the initial localization in the intestines, the invasion of the muscles, and the final encystment. Swine become infected with this parasite by eating scraps of infected meat, or the offal of their own kind, or by eating infected rats. The rat, through its cannibalistic propensities, becomes infected frequently, and is one of the chief factors in the wide dissemination of the disease. Human infection is practically accidental and self-limited; biologically speaking, man as a host does not enter into the calculations of the parasite. Treatment of established trichiniasis infection is palliative, not truly remedial. The parasites, once inside the body, cannot be materially affected by the administration of any drug. While cure of trichiniasis is thus difficult, if not impossible, prevention is very simple. The thorough cooking of all food is sufficient to preclude infection. This relatively simple means of destroying the larvae is a more certain as well as less expensive method of preventing infection than is the laborious microscopic examination of the tissues of every slaughtered hog. In Germany between 1881 and 1898 over 32 per cent of 6,329 cases of trichinosis that were investigated were traced to meat that had been microscopically examined and passed as free from trichinae.[92] On the other hand, thorough cooking removes all possibility of danger. TENIASIS Various tapeworm or cestode infections are contracted by eating meat containing the parasite. Particular species of tapeworm usually infest the flesh of specific hosts, as _Tenia saginata_ in the beef and _Tenia solium_ in the hog. The dwarf tapeworm, _Hymenolepis nana_, develops in rats, and the human infections with this parasite occasionally observed are probably caused by contamination of food by these animals. [Illustration: FIG. 8.--_Cysticercus cellulosae_ in pig's tongue. (After Neumann and Mayer.)]