10 THE ANIMAL PARASITES OF MAN 



by which we may confirm the diagnosis in a great many cases. Such 

 means consist not only in a minute examination of the patient by 

 palpation, percussion and local inspection, but also in the micro- 

 scopical examination of the natural secretions and excretions of the 

 body, such as sputum, nasal mucus, urine and faeces. Though such 

 examinations may entail loss of time, they are necessary in the interest 

 of the patient. It appears, moreover, that quackery, which has 

 gained considerable ground even in the treatment of the helminthic 

 diseases of man, can thus be considerably limited. 



Origin of Parasites. 1 In former times, when the only correct views 

 that existed related to the origin of the higher animals, the mode 

 of multiplication of parasites as well as of other lowly animals 

 was ascribed to SPONTANEOUS GENERATION (generatio cequivoca), and 

 this opinion prevailed throughout the middle ages. The writers on 

 natural science merely devoted their time to the interpretation of the 

 views of the old authors, and perpetuated the opinions of the ancients 

 on questions, which, even in those days, could have been correctly 

 explained merely by observation. 



It was only when observations were again recommenced, and the 

 microscope was invented, that the idea of spontaneous generation 

 became limited. Not only did the microscope reveal the organs of 

 generation or their products (eggs) in numerous animals, but Redi 

 succeeded in proving that the so-called Helcophagi (flesh maggots) are 

 only the progeny of flies, and never appear in the flesh of slaughtered 

 animals when fully developed flies are prevented from approaching 

 and depositing their eggs on it. Swammerdam likewise knew that 

 the "worms" living in the caterpillars of butterflies were the larvae 

 of other insects (ichneumon flies) which had laid their eggs in their 

 bodies ; he also discovered the ova of lice. The two authors men- 

 tioned were, however, unwilling to see that the experience they had 

 gained regarding insects applied to the helminthes. Leeuwenhoek 

 also vehemently opposed the theory of a spontaneous generation, 

 maintaining that, on a basis of common-sense, eggs, or at all events 

 germs, must exist, even though they could not be seen. 



The use of the microscope also revealed a large number of very 

 small organisms in the water and moist soil, some of which un- 

 doubtedly resembled helminthes. Considering the wide dissemination 

 of these minute organisms, it was natural to conjecture that after their 

 almost unavoidable introduction into the human system they should 

 grow into helminthes (Boerhave, Hoffmann). Linnaeus went even 

 further, for he traced the descent of the liver-fluke of sheep from 



1 Die Geschichte der " Klinisch wichtigen Parasiten," behandelt H. Vierordt im " Handb. 

 d. Gesch. d. Med. hrsg." v. M. Neuburger u. J. Pagel, Bd. ii, 1903. 



