There is not the least doubt that human beings are almost exclusively infected with Tænia solium by eating pork containing cysticerci in a condition that does not endanger the life of the cysticerci. The infection may likewise be caused in man by eating the infected meat of other animals subject to this species of bladder worm, mainly, as a matter of fact, deer and wild boar.
The frequency of cysticerci in pigs’ flesh has considerably decreased since the introduction of meat inspection; in the Kingdom of Prussia there was on an average 1 infected pig to every 305 slaughtered between 1876 to 1882; from 1886 to 1889, there was 1 to 551; from 1890 to 1892, there was 1 to 817; in 1896, 1 to 1,470; and in 1899, 1 to 2,102; in the Kingdom of Saxony in 1894 there was 1 infected pig to every 636; in 1895 there was 1 to every 2,049, and in 1896 only 1 infected pig was found of 5,886 slaughtered. In South Germany pigs with cysticerci are very rare, but are more frequent in the eastern provinces of Prussia; in 1892 the number of infected pigs compared with the total slaughtered was as follows:—
| In the district of Marienwerder | 1 : 28 |
| " " Oppeln | 1 : 80 |
| " " Königsberg | 1 : 108 |
| " " Stralsund and Posen | 1 : 187 |
| " " Danzig, Frankfort a. O. and Bromberg | 1 : 250 |
| As compared with the district of Arnsberg | 1 : 865 |
| " " " Coblenz | 1 : 975 |
| " " " Düsseldorf | 1 : 1,070 |
| " " " Münster and Wiesbaden | 1 : 1,900 |
The average for the whole of Prussia in the same year was 1 : 1,290; for the eastern provinces, on the other hand, 1 : 604. Even more unfavourable are the proportions in Russian Poland (over 1 per cent. of pigs measly), in Prague (over 3 per cent.), in Bosnia and Herzegovina (6 to 7 per cent.). The cause for this is most likely attributable to the manner in which the pigs are kept. When allowed to be in the farmyards of the small farmers for the whole day, or allowed to wander in the village streets and pasture lands, they are more liable to take up the oncospheres of the T. solium than when shut up in good pig-styes.
The geographical distribution of T. solium generally corresponds with that of the domestic pig and the custom of eating pork in any form insufficiently cooked or raw. There are, or were, some isolated districts in Germany, France, Italy and England where the “armed tapeworm” was frequent (for instance, Thuringia, Brunswick, Saxony, Hesse, Westphalia, whereas it is and was very scarce in South Germany); it is thus easily understood why it occurs very rarely in the East, in Asia and in Africa, in consequence of the Mahommedans, Jews, etc., not eating pork. In North America, also, T. solium is very rare; the tapeworm which is known there by this name is generally T. saginata, Stiles. During the last decade T. solium infection has, however, very markedly decreased in North and East Germany in consequence of the precautions exercised by the public in the choice of pork to avoid trichinosis, especially, however, because measly meat must be sold as such and must be thoroughly cooked before being placed on the market; indeed, if badly infected it may not be sold for food, but can be turned to account for industrial purposes.
The occurrence of Cysticercus cellulosæ in man has been known since 1558 (Rumler, Obs. med., liii, p. 32); there is hardly an organ in man in which cysticerci have not been observed at some time; they are most frequently found in the brain,[289] where they grow to a variety known as Cysticercus racemosus; next in frequency they are found in the eye, in the muscular system, in the heart, in the subcutaneous connective tissue, the liver, lungs, abdominal cavity, etc. The number of cysticerci observed in one man varies between a few and several thousands. Of the sexes, men are most subject (60 to 66 per cent. of the number attacked). The disturbances caused in man by cysticerci vary according to the nature or position of the organs attacked; when situated in the cerebral meninges they have the same effect as tumours.
During the last decades, however, these cases have also become less common. In Rudolphi’s time 2 per cent. of post-mortems in Berlin showed cysticerci; in the ’sixties, according to Virchow, about the same; in 1875 the number fell to 1·6 per cent.; in 1881 to 0·5 per cent.; in 1882 to 0·2 per cent.; in 1900 to 0·15 per cent., and in 1903 to 0·16 per cent. Hirschberg between 1869 and 1885 discovered cysticerci in the eye seventy times in 60,000 ophthalmic cases, but during the following six years the parasite was only present twice amongst a total of 46,000 cases of ophthalmic diseases, and since 1895 no ophthalmic case has been met with.
The infection of human beings with the cysticerci can only take place by the introduction of the oncospheres of Tænia solium into the stomach with vegetable foods, salads that have been washed in impure water containing oncospheres, also by drinking contaminated water; the carriers of T. solium, moreover, infect themselves still more frequently through uncleanliness in defæcation, the privies in public localities and many private houses affording striking testimony of this. The minute oncospheres can thus easily reach the fingers and thence the mouth (as in twirling the moustache, biting the nail). More rarely a third manner of transmission or internal auto-infection may possibly take place, as when, in the act of vomiting, mature proglottids near the stomach are drawn into it; the oncospheres or segments there retained are then in the same position as if they had been introduced through the mouth.
On account of these dangers of internal or external auto-infection, it is therefore the duty of the medical attendant, after recognizing the presence of tapeworms, to expel them,[290] and in doing so to employ every possible means to prevent vomiting setting in; it is, however, equally important to take the necessary steps to destroy the parasites evacuated. It may be incidentally mentioned that in using certain remedies the scolex not rarely remains in the intestine; the cure in such cases has not been accomplished, as the scolex again produces new proglottids, and after about eleven weeks the first formed ones are again mature and appear in the fæces.
Amongst the cysticerci also many malformations appear; thus absence of the rostellum and the hooks, or double formation with six suckers, or abnormalities of growth on account of the surroundings, which have had a special name given to them, viz., Cysticercus racemosus, Zenk. (= C. botryoides, Hell.; C. multilocularis, Kchnmstr.); these forms are more especially found at the base of the brain, are irregularly ramified and often without the head.