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sions reached. All of the animals included in the statistical results came from the city of Lincoln, although it is evidently impossible to say that all of them had long been residents of this place. Among the animals which were examined were representatives of all the varied conditions of life under which these forms are found, from the half-wild strays of city streets and alleys to the pets accustomed to the luxury of a home. I shall consider first the results from the study of the dog, and later those which bear on the parasites of the cat. Table A indicates the degree of infection of the dogs examined, and table B the kind of parasites,
together with the frequence of each. For comparison with this I have records of only two dogs from any other part of the state. These were examined at Table Rock by one of my students. One individual contained a dozen specimens of Taenia serrata, and the other harbored one hundred fifty-two of the same species, but no other parasites were found in either. To compare the results of similar examinations that have been made in other parts of the world I have compiled a table, given by Deffke, with the addition of recent investigations made in Washington, D. C., and in Lincoln.
It is interesting to examine critically the results shown by the table; among the parasites the following groups are represented: Trematodes by one species in adult condition.
Cestodes by nine species in adult condition, and also two species in larval condition.
Nematodes by five species in adult condition.
Acanthocephala by one species in adult condition.
Linguatulida by one species in adult condition.
Insecta by one species in larval condition.
We may dismiss at once the first and last three groups, since the occurrence of the parasite is occasional at most and not productive of serious results to its host and since, furthermore, the species are not transmitted to man or to any important domesticated animal so as to occasion disease or death. The larval Cestodes may also be set aside for similar reasons; their presence in the dog is certainly accidental.
Among the Nematodes, however, are forms of considerable importance. Ascaris mystax, the most abundant and most widely distributed species, occurring in about one-quarter of all the dogs examined, is the common "stomach worm" of dogs and cats. It occurs rarely also in man, where its accidental introduction is undoubtedly due to the presence of infected dogs or cats in the house. Uncinaria trigonocephala is neither so widely distributed nor so abundant as the foregoing species. When present in large numbers it is the cause of a serious disease among hunting dogs, but cannot be transmitted to man. other nematode parasites listed are of minor importance.
Both in number of species and of individuals the Cestodes far outweigh all other canine parasites. They include also the dangerous forms, and hence deserve particular attention in the present discussion. Of the nine species of adult tapeworm listed as found in the dog it may be said that Taenia serrata does not occur either as adult or as larva (Cystercercus) in the human system. Taenia marginata has been said to occur in man in its larval condition (Cysticercus tenuicollis), but the weight of the authority seems to disprove this statement and to demonstrate that these are cases of incorrect determination of the species of parasite found. Taenia coenurus is also foreign to man; it is, however, of great hygienic importance, since it is the cause of the so-called "gid" of sheep, a disease which in some parts of the world entails a serious loss to sheep raisers. It will be noticed that the species is not known to exist in America as yet. Taenia serialis is a rare form at most; it has been met in Europe and in Washington,
though not included in the lists tabulated. It is not known to be of pathological importance. Dipylidium caninum is found in man rarely, and usually only in children of immature years, among whom it seems to be not very uncommon. The intermediate host is the dog-flea and the infection comes through the accidental swallowing of some of these parasites, which have come from a pet dog of the house. This, of itself, is sufficient reason for training children to avoid fondling household pets, at least in such an intimate way as is frequently seen.
There remains to be considered, then, merely the single species Taenia echinococcus. The adult form, which lives in the intestine of the dog, is an insignificant tapeworm, consisting of only three or four segments and having a total length of not more than 5 mm. Its larval form, however, the hydatid, known as the Echinococcus, which in its various forms has received something like a dozen different specific names, is the most insidious and dangerous parasite which inhabits the human system. It will easily be seen how serious an evil the presence of the adult in the dog must be regarded, since the eggs thus set free from the canine intestine would be scattered here and there with the dust of the dwelling or its immediate surroundings, and would thus easily by chance reach in the intestine of a human host and there be hatched out; the larva would pass to some point in the abdominal cavity, there to attain gradually its enormous development with probable fatal results to the host. It is certainly fortunate that this form is so rare in America as not to have been found in the course of the systematic investigations quoted here. It does, however, occur, since the adult has been found in Washington on at least one occasion. Sumner has also listed 100 cases of the occurrence of the Echinococcus disease, which are recounted in the various medical publications of the country for the last fifty years.
Having thus considered the characteristics of each species of the more important dog parasites, let us review a few facts with reference to the frequency of these forms in our own country. It will be noticed that Iceland and Australia are the only locali
ties for which investigations have been made, that show a larger percentage of dogs infected than was found in Lincoln, while the number infected in Denmark, Prussia, and Saxony is decidedly less. A closer study of the table also shows, however, that the high percentage of dogs infected in Lincoln is due to the extraordinarily large number of hosts that harbored Taenia serrata and Dipylidium caninum. With reference to the first of these, Lincoln dogs were three times as frequently infected as those from any other part of the world and very many times more than those from most regions listed. With reference to Dipylidium it will also be noticed that it is present in a somewhat larger per cent. than is found anywhere in the world, and in a decidedly greater percentage of dogs than is shown for almost all places. So far as the other species of parasites are concerned, there is, in the first place, at least as small a percentage as in others, and the species which have already been designated as peculiarly dangerous to the health of man, or of some of the domestic animals are entirely lacking, so far as the limits of the investigation go. In other words, though the total percentage of dogs infected is larger than has been found in most places, yet the most dangerous parasites seem to be entirely lacking, and the excessive total percentage is due to an unusual number of two species in particular, which are not to be regarded as dangerous parasites. So far as the Washington dogs are concerned, the total percentage is again very much greater than in most places. This is due, not to the presence of the more dangerous forms, but to large numbers of forms which, in themselves, are comparatively harmless. Regarding only the more recent, and presumably more careful examinations, those listed in the last four lines of the table, it may be said that the number of kinds of the parasites found in the various parts of this country is only about two-thirds as great as the number of varieties reported from Germany. If it be asked, then, what are the causes which give us, on the one hand, a large percentage of harmless parasites, and on the other, excessive rarity or entire lack of the more dangerous forms, I believe that some part of the answer