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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



But the " broad-head " is, moreover, found to 

 affect certain districts or regions within this Eu- 

 ropean area, so that its distribution in Europe is 

 itself of peculiar kind. Its headquarters appear 

 to be the cantons of Western Switzerland and the 

 nearest French provinces. It affects Poland, Rus- 

 sia, and Sweden, in the north and northwestern 

 parts, and it also occurs, but less typically, in 

 Holland and Belgium. In Eastern Prussia and 

 Pomerania the " broad-head " has occasionally 

 appeared ; but the latter districts are probably to 

 be regarded in the light of occasional habitats 

 rather than of stated and permanent kind. 



The reasons for the restriction of the para- 

 site to such a limited field are by no means clear. 

 We are not yet sufficiently acquainted with its 

 development and life-history to make generaliza- 

 tions, but one significant fact remains to be noted, 

 namely, that the " broad-head " flourishes in the 

 regions in which the common tapeworm is an un- 

 known or comparatively rare visitant. Now this 

 observation is exactly paralleled by the peculiari- 

 ties of the distribution of higher animals. Iu 

 one country we may find what are termed " rep- 

 resentative species " of the animals which occur 

 in another and distant region. Thus the puma 

 in the New World assumes the place of the lion of 

 the Eastern Hemisphere ; the tapirs of the East- 

 ern Archipelago are balanced in the opposite side 

 of the world by the American species ; and the 

 llamas of South America represent their camel- 

 neighbors of the Old World. There thus appears 

 in such cases to be a balancing of animal life : 

 the one species in one region or continent as- 

 suming the functions of the nearly-related but 

 different species inhabiting another area of the 

 world. Regarding the case of the parasites in 

 this light, we may deduce a similar conclusion, 

 namely, that the " broad-head " may discharge in 

 its especial field of action the functions performed 

 in other fields or areas by the commqn tapeworm. 

 Nature, in any case, may certainly be credited 

 with the general avoidance of any confusion of 

 interests, and with the exclusion of rivalry from 

 the domain and functions of like or nearly-re- 

 lated creatures, wherever that domain may exist, 

 and whatever these functions may be. 



As a final example of a most singular and at 

 the same time utterly harmless little intruder on 

 the human domain, may be mentioned the mi- 

 nute mite known to naturalists as a species of 



Dcmodex, and which, curiously enough, seems to 

 take up its abode in the ducts or " follicles " of 

 the skin at the sides of the nose. It is highly 

 probable that this little creature is very fre- 

 quently to be found in the situation just men- 

 tioned, its minute size and harmless character 

 preventing our being made aware of its mere ex- 

 istence. Demodez measures a mere fraction of 

 an inch in length, and may be said to present us 

 with yet another instance of an organism whose 

 selective powers in the choice of a habitation 

 appear to be of the most singular descrip- 

 tion. 



The lessons to be drawn from a consideration 

 of the entire subject of the parasitic enemies of 

 man bear very strongly on questions of common 

 hygiene and sanitation. The extension of our 

 knowledge of parasites and of their life-histories 

 clearly points to the desirability for the exercise 

 of great care in the choice and preparation of our 

 common foods, especially of animal kind. Un- 

 cooked animal food in any form should be unhes- 

 itatingly rejected on common sanitary grounds, 

 the prevailing and fashionable taste for "under- 

 done" meat notwithstanding. The Mosaic ab- 

 horrence of the pig is fully justified by an appeal 

 to zoological knowledge regarding the parasites 

 to which that familiar and not uninteresting 

 quadruped plays the part of entertainer and 

 host; but the due exercise of the culinary art 

 should in large measure mitigate the severity of 

 the sentence passed against pork as a common 

 medium of parasitic infection. Unwashed vege- 

 tables, which may harbor or lodge, without de- 

 veloping, the embryos of parasites, are similarly 

 to be regarded with suspicion. Indeed, it may 

 be said that the chances of parasitic infection 

 from this latter source are greater than those 

 from badly-cooked meat, the vegetable matter 

 escaping even the chance of having its minute 

 tenants destroyed. Unsavory as the subject may 

 at first sight appear, the whole question before us 

 teems with an interest which should effectually 

 appeal to every one in the light of saving knowl- 

 edge. And it is not the least worthy remark 

 which may be made regarding such a topic, that 

 zoological science may be shown capable of ex- 

 tending its interests into the most intimate de- 

 partments of the household, and even of encroach, 

 ing on the sphere of that domestic autocrat, the 

 cook. — The Gentleman' 1 s Magazine. 



