558 MUSUUAVE, CLEGG, AND POLK. 



Air, clothing, dust and other substances may be considered as possible factors 

 in the spread of the infection in a mechanical way. 



Animals. — Several authors have called attention to the possible inflence of 

 animals in the transmission of this infection. When it is remembered that some 

 domestic animals used as pets may harbor this parasite, and that from their 

 habits several of them are likely to have the eggs in their hair, it would seem 

 that animals might be expected to be occasional transmitters of the infection, 

 particularly among children. 



Pathogenicity. — The largely accepted commensalism of this parasite 

 is not in accord with the majority of the carefully reported observations 

 (see literature review), nor is it borne out by study of our cases. Belief 

 in the harmless character of Trichwis is based largely upon two ob- 

 servations: first, the great, general prevalence of the parasite without 

 symptoms, and second, no satisfactory explanation of the nature of its 

 pathogenic action has been offered. 



If we examine the first of these in comparison with some other para- 

 sitic infections we find it to be a difference in degree only and not a 

 peculiar condition. For example, Uncinaria are accepted as pathogenic 

 parasites and 3'et in our service more than 90 per cent of individuals 

 harboring the worm show no symptoms whatever of the infection. The 

 first symptoms of infection with amoeba? may be those of peritonitis from 

 a perforating ulcer, 



Strongyloides stercoralis is now generally accepted as a pathogenic 

 parasite, and yet in the vast majority of instances no symptoms are pro- 

 duced by its presence, and similar statements may be made regarding 

 Balantidium coll, Dibothriocephalus lotus and a number of other parasites 

 usually accepted as pathogenic. 



The percentage of cases infected with Trichwis without symptoms 

 probably is greater than for any of the above-named parasites, but in- 

 fections do occur which produce symptoms and the degree of difference 

 does not appear to be great enough to justify it as an argument for the 

 commensalism of Trichwis. 



As to the second of the two views, that no satisfactory explanation of 

 the nature of the infection has been made, we may at least in part answer 

 that here the difference from some of the other parasites is also one of 

 degree. No satisfactory explanation of the exact manner of the produc- 

 tion or character of the lesions, produced by the majority of the intestinal 

 parasites of man, has been offered. 



The pathogenic character of Trichuris has been explained by consider- 

 ing it to be a blood sucker; by believing it to produce a hemolytic sub- 

 stance such as is also acredited to hook-worms; by the formation by it of 

 a toxin; by mechanical action and by its producing perforations which 

 open a way for the entrance of bacteria. None of these explanations is 

 supported by sufficient data to justify its acceptance. The majority of 

 the repeated statements that the parasite is a blood sucker are credited 



