From a biological standpoint parasites constitute a group of great importance. The forms included under the term are members of widely separated families which have acquired similar habits and by virtue of like conditions in their environment have manifested convergent variation, departing at times so widely from the primitive type that their relationship was long misunderstood and in numerous instances is even yet a matter of doubt.
   These forms are, however, of no less economic importance since they are responsible for some of the serious ailments which fall upon man and his closest allies, the domesticated animals. From both standpoints, then, the group of parasites deserves the closest study, and yet, despite its importance, but little has been accurately determined concerning the distribution and frequence of these forms in our own country.
   The intimate relations in which the domestic animals stand to man have always made the transfer of parasites from one to the other a matter of much greater probability than exists between man and other forms of animal life. It is but natural that the most common species of human tapeworm come to man from his two chief sources of animal food, beef and pork. The chances of accidental infection, however, are evidently much greater in the case of those forms that are intimately associated with man, and hence clearly greatest in those which he holds as household pets, the dog and the cat. It is also evident that the chances of parasitic infection are greatest in the case of those peoples or individuals who live on terms of closest intimacy with these domesticated forms. Thus, the Icelander, who is known to permit his dog to occupy, not only the same room, but even the same
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bed with himself, is most seriously troubled with the parasites common to dogs and man, and the infant or child is more likely to be infected than persons of maturer years. It becomes, then, a matter of great importance to determine in any region or community what is the average percentage of these animals infected with parasites, since, as will be evident later, the percentage of infection varies widely in different regions. It is, however, by no means a matter of indifference what parasites occur in the dogs or cats of a specific locality, for certain of the species are entirely foreign to the human race, not being known to be at home in man at any stage of his existence, and certain species are comparatively harmless, even when present, while certain others are the causes of grave disorders, among them the most serious parasitic disease which is known. In a paper on the prevalence of Entozoa in the dog, and their relation to public health, published in 1807 by Dr. Cobbold, of London, perhaps the most eminent helminthologist that England has ever produced, the author emphasizes again and again the importance of helminthological studies on this animal, and the necessity of extended knowledge concerning the number and kinds of its parasites. It seems, then, of importance to ascertain for Lincoln the extent to which its canine population is infected as well as the species of parasites which occur in dogs here. The cat, although not so closely associated with man and not furnishing him with so many species of parasites, has also been included within the limits of this investigation. During the last three years a large number of animals of both species have been carefully examined for parasites and the results of the examination recorded. For kindly assistance in this work I am indebted to a considerable number of students, who have been connected with the University during this time. The final examination and determination of the parasites, as well its the tabulation and discussion of the same, are the results of my own study. Many other animals of these species have been examined in part, or, owing to circumstances, with less care; they have not been considered in the tabular results given, although no facts have been observed which do not bear out the conclu-

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

   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. Asearis mystax, the moat, 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. The 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. Tacnia inarginata 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 seem 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 nun. Its larval form, however, the hydatid, known as the Echinoroceus, 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 Dipylidiun caninum. With reference to the first of these, Lincoln dogs were three times am 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

at least may be given at once. The recent settlement of this part of the country, and the uncontaminated condition of fields and pasture lands is undoubtedly a reason for the existence of a less number of parasites than are found in the longer settled portions of the world. But in addition to this, and--I am inclined to think--of even more importance, is the general prevalence, in this western country at least, of the large slaughter-houses.
   According to the primitive method of slaughtering which was in general vogue throughout the country a few years ago, and which is still practiced in many of the more conservative portions of the country, animals were slaughtered on the farm, or in some temporary slaughtering house, and the remains were thrown to dogs or hogs as the easiest way of getting rid of them. In this way the larval forms reached their final host and the number of parasites was unquestionably augmented.
   Under present conditions the various parts of the animal are utilized to such an extent that, as the packers say, "The only part of the hog which goes to waste is the squeal." By this means all of the larval stages, particularly of the tapeworms, which are present as bladder-worms in the omentum or in the connective tissue of various parts, are destroyed and never reach their ultimate host.
   Thus it is that T. marginata, T. coenurus, and T. echinococcus are so rare here as to be almost lacking. It is evident also that with the more perfect methods of slaughtering and more complete utilization of the fragments, the number of stages of larval tapeworms which reach the final host will be still further diminished, and the danger from such parasites proportionately removed. In Berlin, Germany, it has been shown by Deffke that a reduction in the number of canine parasites has taken place since the introduction of compulsory meat examination, and the destruction of infected portions of all animals slaughtered.
   A further support to this opinion seems to be found in the abundance of Taenia serrata in dogs obtained in Lincoln. The larva of this parasite is a bladder-worm (Cysticercus pisiformis) found abundantly in the rabbit; the latter is not only extremely

common in this region, and frequently hunted by dogs as a matter of mere sport, but also if used as human food, dressed at home or in smaller butcher shops, where the refuse easily falls in the way of dogs of all kinds. Thus not only the natural hunting proclivity of the dog, but the element of chance as well, favors the increase of this particular species of parasite.
   It may, then, be properly affirmed that although the dogs in this country are apparently more seriously affected with parasites than their relatives of modern Europe, they are yet not such a menace to public health, since the parasitic species peculiarly dangerous to the human family at least are either wanting or extremely rare. This, however, does not mean that intimate association with the dog tribe is more worthy of encouragement here. If for no other reason than the extreme abundance of Dipylidium caninum it would be best to limit the association of dogs and children, since this form is a comparatively frequent parasite of man in his earlier years.
   The records which have been kept of parasites of cats, including those that have been subject to a complete examination during the past three years, are also given in the two following tables (C, D). As compared with the dogs it will be seen in the first place that fewer cats are free from infection, and in the second, that a smaller number of species of parasites has been taken from the cat than from the dogs of this region. Again, the total number of parasites present in any one individual falls far short of that found in some of the dogs. Thus the largest total number of parasites taken from any cat was less than sixty, whereas

four dogs out of twenty harbored from two to five hundred parasites each. Furthermore, twelve of the nineteen infected cats contained each but a single species of parasite, whereas twelve of the fifteen infected dogs yielded more than one species of parasite from each host.
   The species of parasites found in cats include the following groups:
   Trematodes, represented by one species in adult condition.
   Cestodes, represented by two species in adult condition.
   Nematodes, represented by two species in adult condition.
   These results are also in strong contrast with those obtained from dogs. The number of groups represented is smaller and no one has an evident superiority over all others. It is interesting to note that the only Nematodes which occur are common to the dog also, and that in fact but two of the five parasites listed do not also occur in the dog in Lincoln. The cat has thus neither any very abundant nor any peculiarly characteristic parasites. And among those which it does harbor there are none which induce in it or in other domestic animals any serious disease.
   So far as man is concerned there are two species of parasite listed here which may be found in the human system, though neither is of prime importance in this connection.
   Of these two parasites of cats, Dipylidium caninum has already

been discussed as an abundant parasite of the dog. Distoma felineum, which is the most abundant parasite of cats in this region, has been reported from Siberia as a frequent human parasite. It should be stated that the two forms are possibly not the same species, but are certainly so closely related that this species may also well be a parasite of man under favorable circumstances. The other feline parasites are not found in man. I regret to state that extended search has not discovered tables giving the frequency of parasites of cats in other parts of the world so as to afford basis for comparison with the results obtained here. It would then be hardly more than a guess as to whether the conditions represented here are favorable or unfavorable.

Zoological Laboratory,
   The University of Nebraska.

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