EAKLY VIEWS ON PARASITIC DISEASES. 121 



anatomy; on the other, the natural desire to reduce the different 

 diseases to definite etiological entities. Men then hit upon parasites, 1 

 as they did later upon magnetism and electricity, in part only because 

 they knew so little about them. 



It occurred to them the more naturally to refer these diseases to 

 parasites when they observed the exit of intestinal worms and conse- 

 quent recovery; and also because, since the time of the Arabian 

 physicians, the parasitism of a mite had been recognised as the cause 

 of the widely distributed itch (see Fig. 6). In the eyes of many patho- 

 logists, the last-named fact served as direct proof of the correctness of 

 a theory from which they anticipated the weightiest conclusions as to 

 the nature of diseases. 



But these hopes were vain. Although helminthological knowledge 

 was gradually more and more extended and consolidated, the idea of 

 the " Morli animati " found no new support. Men attempted in vain 

 to place beyond doubt the existence of a Contagium vivum in the 

 above-mentioned diseases. They only formed the conviction that the 

 earlier physicians, with their guesses at the existence of certain para- 

 sites, had been much too generous. The so-called "heart-worms" 

 were recognised as blood-clots, the " umbilical worms " as mere 

 fancies. The existence of the itch-mite even was doubtful, since 

 a number of experienced physicians and naturalists had sought after 

 it in vain. Observations concerning the presence of intestinal worms 

 in animals also increased, in which, in spite of this parasitism, no 

 signs of illness were noticed. 



Under such circumstances, the earlier opinions became in the 

 latter half of the last century more and more discredited. 



The Entozoa were still, it is true, considered on the whole as in- 

 jurious guests, which might seriously affect the health, and sometimes 

 even endanger the life of their host. But their specific relations to 

 certain diseases gradually ceased to be traced ; and there were many 

 who even denied that intestinal worms had any hurtful effects on their 

 host whatever ; some even considered their effects to be advantageous. 

 Men like Goze and Abildgaard maintained among other views that 

 intestinal worms aided digestion, by absorbing the mucus and ex- 

 citing peristaltic contractions. Jordens even called them the good 

 angels and unfailing helpers of children. 2 It was also supposed (e.g., 

 by Gaultier) that their movements and the resulting conditions ex- 

 erted a favourable influence on the development of the lungs and 

 viscera. 



1 These speculations went so far, that this question, for example, was discussed (and 

 answered mostly in the affirmative) " An mors naturalis sit substantia verminosa ?" 

 - " Entomologie und Helminthologie des inenschlichen Korpers :" Hof, 1801. 



