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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, favor's 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.
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.