162 THE EFFECTS OF PARASITES ON THEIR HOSTS. 



I have, indeed, expressly stated (p. 85) that certain individual 

 characteristics, such as age, exercise a distinct influence on the de- 

 velopment of the imported germ ; but at the same time I believe that 

 the majority of cases cited in support of the theory of a definite 

 liability, will admit of another interpretation. When, for example, 

 we find that children are more frequently infested by thread-worms, 

 or by Tcenia cucumerina, than adults, and that they are but rarely 

 subject to the common tape-worm, that does not denote, in my 

 opinion, that children 1 have a greater disposition to the first-men- 

 tioned worms, but only that they have, in the natural conditions of 

 their life, much more opportunity to infect themselves with the larval 

 stages of these parasites. I need only urge in support of my con- 

 tention that children eat or suck all sorts of things without choice or 

 distinction, and have therefore abundant opportunity to infect them- 

 selves with various transmitters of parasites, with which they would 

 not, under ordinary circumstances, come into contact. 



In the same way we may explain the very abundant occurrence of 

 parasites which Vix has lately shown to be attendant on those mental 

 diseases which are characterised by voracity. The "dirt-eating," 

 which Vix would regard as a consequence of the helininthiasis, seems 

 more probably the cause of it. 



Nor is it, of course, a sign of a special " predisposition " that the 

 female sex suffers more frequently (in the proportion of two to one 

 according to Wawruch) from Tcenia saginata and T. solium, since the 

 household duties of women expose them to a much greater danger of 

 infection by cystic worms. If not, we must consistently credit cooks 

 and butchers with a similar disposition to tape-worm, and even to 

 sporadic trichinosis, since they are of all persons most troubled by 

 these parasites. 2 It is the trade which explains the frequency, just 



1 According to Gribbohm (loc cit., p. 7), the per-centage of children below ten suffering 

 from Ascaris is 24*6, as compared with an average of 18*3. Similarly, as regards Ojri/uri*, 

 the per-centage is 31 "6, as opposed to the average 23 '3 ; and in the case of Trichorcpkalus, 

 33 '3, as compared with 32*2. The total number of children below twenty infested with 

 intestinal Nematodes is not less than 62 per cent, while the average for all ages is 

 only 43 '5. The number of the cases used as a basis of calculation (Gribbohm bases his 

 conclusions on 1117 post mortem examinations) is, of course, much too small to give certain 

 results. In this way, we can understand how Muller, depending on the statistical results 

 of the Dresden and Erlangen Hospital (" Zur Statistik der menschlichen Entozoen," 

 Erlangen Dissert., 1874), contradicts the commonly received opinion, by stating that 

 Ascaris and Oxyurls are not, on the whole, more frequent among children than among 

 older persons. We may further note that Tcenia cucumerina has only been observed in 

 children and never in adults. 



8 This observation dates from the beginning of this century, and seems to have been 

 first made by Fontassin. Wawruch, to whom we owe the most extensive information as 

 to the statistics of the tape-worm, found that of 206 patients more than a quarter belonged 

 to the above occupations. 



