IN THE BODIES OF ANIMALS. 381 



indeed, on the authority of Rudolphi, no class is exempt, for 

 the vermes themselves are liable to their depredations ; and I 

 believe we are yet ignorant of the limit to the application of the 

 doctrine of " vive inter vivas." That the existence of parasi- 

 tical worms should long have been known and observed is not 

 surprising, for they are constantly obtruding themselves on our 

 notice, in the every- day operations of the anatomist, compa- 

 rative and human, the butcher and the cook. The Billingsgate 

 fishwoman can tell us a long history about them ; for, if in 

 any class of animals they superabound, they seem to do so in 

 the fish. Coextensive with the discovery of these creatures in 

 the different parts and organs of animals, has been the inquiry, 

 Whence their origin ? and to the solution of this difficulty 

 the minds of men have been directed from a very early period ; 

 it is not my intention, however, to enter into an examination of 

 the crude notions which have from time to time been enter- 

 tained on this subject, although we might possibly derive 

 some amusement from doing so, nor to examine into the 

 favourite doctrine of the ancients, spontaneous generation on 

 the one hand, or that modification of it entertained by some of 

 the moderns on the other. 3 It is now two years since I first 

 gave this subject much consideration, when I instituted 

 experiments, with the hope of throwing some light upon 

 it; how far I have succeeded in this remains to be seen 

 in the sequel. Upon a superficial view of the inquiry, it 

 evidently divides itself into two branches — either that the 

 source from which worms are derived is an extrinsic one, or 

 that they are spontaneously generated within the animal which 

 they infest. The latter I am unwilling to admit : let us examine 

 the facts which favour the former opinion ; and first, do they 

 gain access through any of the mucous canals ? This view of 

 the matter has met with many advocates, some of whom have 

 hastily adopted it as the most probable ; others, from the 

 supposed observation of parasitical animals in situations exterior 

 to the body. Rudolphi objects strongly to this method of 



a It is not an uncommon idea, in many parts of the country, that the seeds of 

 gooseberries are the eggs of worms ; and, in proof of it, we are asked to account 

 for the prevalence of the verminous diathesis during the gooseberry season in 

 any more probable manner! And I have heard it gravely asserted that the 

 liver fluke-worm, Destoma hepaticum, is the offspring of the seeds of the Ranun- 

 culus flammula, or Ranunculus acris .' Hasty induction is the most fruitful source 

 of error, and often leads men to confound the propter hoc with the post hoc. 



