The parasites of man, and the diseases which proceed from them : a text-book for students and practitioners / by Rudolf Leuckart ; translated from the German, with the co-operation of the author, by William E. Hoyle.

Date:
1886
Catalogue details

Licence: Public Domain Mark

Credit: The parasites of man, and the diseases which proceed from them : a text-book for students and practitioners / by Rudolf Leuckart ; translated from the German, with the co-operation of the author, by William E. Hoyle. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    analogous to stationary parasites. I only need to mention certain caterpillars and other insect larva?, many of which lead a stationary lite like the intestinal worms, and, furthermore, resemble them in that, in many cases (e.g., ichneumon-flies, &c), they are occasionally or even constantly parasitic. Besides these negative characters, stationary parasites can in many cases be recognised by positive characters, such as the possession of hooks and suckers, which serve to fix them on to the body of their host. Structures of this kind are by no means con- fined to stationary parasites, but are also commonly found in temporary parasites, and occasionally even in free-living animals, where, however, they are never so conspicuous or so constantly de- veloped. The more the power of locomotion in a parasite diminishes, the more difficult it is for it to migrate to another animal, and it must therefore be provided with organs which will enable it to retain its position under the most adverse circumstances. These organs of attachment vary in character, in correspondence with the structure of that part of the body of the host upon which the parasite dwells,— being generally stronger and larger in those forms which are parasitic upon the outer skin than in those which live in the interior of the body of their host. Among internal parasites, again, the organs of attach- ment are generally more developed in those species which live in the alimentary canal, since they have to withstand the pressure of its contents. Many intestinal worms, however, do not possess any hooks or other organs of attachment; but in these cases there is gene- rally some compensation. Among the thread- worms, for example, which we shall presently consider, the form and length of the body seem quite as fit to break the pressure of the intestinal contents as to strengthen its hold upon the intestinal wall. In Triclwce'plialm (Fig. 3) the whiplash-like anterior part of the body is actually imbedded in the mucous membrane. In this case the form of the body in a certain way makes up for the absence of proper organs of attachment. When these are present we find the greatest differences in their structure and arrangement, which correspond always to the needs and cir- cumstances of the individual parasite. Some- times, as in the flukes (Fig. 1), muscular suckers are present, which work by atmospheric, or, more correctly speaking.by hydraulic pressure; FlG. 1. —Distomum In- teum (young), with suckers and viscera (after de la Valette).