

INTRODUCTION. 



CHAPTER I. 



UPON THE ORIGIN OF INTESTINAL WORMS. 



HAVING been occupied for many years with inquiries into the 

 natural history of the intestinal worms, a subject involved in 

 much obscurity, I have gradually arrived at the decided conclusion 

 that these parasites do not originate, as has been commonly 

 believed, by "equivocal generation," from substances of a dis- 

 similar nature. With the usual exaggeration and misuse of 

 language, the doctrine of equivocal generation has been applied 

 both to the infusoria and to the intestinal worms. It was diffi- 

 cult, at first sight, to account for the origin and reproduction of 

 these animals, and, even upon closer investigation, they presented 

 many phenomena which could not be recognised in the organiza- 

 tion and vital manifestations of other, especially of the higher 

 animals ; but instead of seeking for the cause of these exceptional 

 peculiarities, people, accommodating themselves to the usually 

 accepted view as to the natural history of these lower creatures, set 

 the matter straight in their minds, by supposing that the unusual 

 phenomena occurred somehow or other in that way ; thus allowing 

 the imagination to indulge in fancies of the wi Ldest description, and 

 even in opposition to the most important laws of nature. It was 

 in this manner that physicians and naturalists thought themselves 

 justified in assuming, that the parasitic worms in the intestines 

 of men and animals owed their origin to ill-digested nutriment, 

 or that they were developed in the most widely different organs 

 from corrupt juices. They took it for granted, that certain 



