124 THE EFFECTS OF PARASITES ON THEIR HOSTS. 



refer especially to the experiments made with Taenia ccenurus'^ and 

 Trichina spiralis, which may well dispel all doubt on the subject. If 

 favourably situated, a brood of these parasites acts like poison, and a 

 large dose is sure to kill the animal. 



Through these experiments, not only has a foundation of fact been 

 laid for the study of parasitic diseases, but an exact method of treat- 

 ment has been attained. While little progress has as yet been made 

 in this direction, we have nevertheless established many new and 

 practically important facts. 



In speaking of parasitic diseases, we mean the various disturb- 

 ances of health occasioned by these creatures, in contradistinction to 

 the views of those who speak as if there were only one "worm- 

 disease " — a specific helminthiasis. 



Parasites act in very different ways,^ according to their size and 

 mode of life, as also according to the nature of the inhabited organism. 

 Intestinal parasites produce different symptoms from brain parasites, 

 and the effects of these are different, according as they are situated in 

 the cortical layers of the hemispheres, or in the crura cerebri. In the 

 same way, Dochmiics duodenalis acts differently from Oxyuris or 

 Trichina. The effects of many parasites never fail — as, for example, 

 in the case of Gysticercus in the eye and Strongylus in the kidney ; 

 and in the case of others, accidental causes determine whether or not, 

 and in what degree, these effects shall show themselves. Besides the 

 situation of the parasite and the individuality of the host, the number 

 of imported germs in this connection is specially important, and to 

 this, indeed, the effects produced and the dangers incurred are ever 

 proportionate. Thus, it can be easily proved that the frightful 

 symptoms of trichinosis occur only when the parasites live in masses 

 in the alimentary canal, and thence invade the muscles^ in still 



1 Especially instructive on this subject is the result of a feeding experiment which 

 was made simultaneously in May 1854 by van Beneden in Louvain, Eschricht in Copen- 

 hagen, Gurlt in Berlin, and by myself in Giessen, with specimens of Tmnia ccenurus sent 

 us by KUchenmeister (then in Bautzen). The animals became ill in all the places at 

 exactly the same time, and exhibited exactly the same symptoms. Compare Haubuer in 

 Gurlt's Magazine, he. cit., Leuokart, " BlasenbandwUrmer," p. 47, or van Beneden, 

 Comptes rendus, t.xxxix., p. 46, 1854. 



' We may take this opportunity of referring to the classical work of Davaine, 

 ' ' Traits des entozoaires et des maladies vermineuses de I'homme et des animaux domes- 

 tiques " — Paris, 1860, 2d ed. 1877 — which contains an almost complete collection of ex- 

 periments concerning worm-diseases up to date, and is full of interesting particulars. The 

 part of this work treating of natural history is not so good even in the second edition, 

 and contains many errors and anachronisms. 



" The number of muscle TncMnai in an individual case has been estimated at from 

 60,000,000 to 100,000,000 — a number which, on the supposition that half of the Trichina: 

 are females, and produce on an average 1500 embryos, would correspond to from 100 000 

 to 120,000 sexually mature animals. 



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