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PARASITIC DISEASES 



feeding-experiments on animals. By this method, 

 and by this alone, their life-history was discovered. 

 They were known to Aristotle and to Hippocrates ; 

 but nothing was understood about them. They 

 were never studied, for this among other reasons, 

 that men believed in spontaneous generation ; and 

 the presence of lower forms of life inside human 

 bodies was attributed to the fault of the patient, 

 or the work of the devil. Then, at last, Redi (1712), 

 and Swammerdam (1752) in his Bibel der Natur, 

 struck at the doctrine of spontaneous generation, 

 saying that it did not apply to insects ; and in 

 1 78 1 Pallas boldly declared that the internal para- 

 sites of man came out of eggs, like insects, and 

 not "of themselves." It would be a good theme 

 for an essay — The paralysing effect, on medicine 

 and surgery, of the doctrine of spontaneous genera- 

 tion. Rudolphi (1808) and Bremser ( 1 8 1 9) opposed 

 Pallas; and von Siebold (1835) and Eschricht 

 (1837) supported him. Then came the great 

 students of this part of biology — Cobbold, Busk, 

 Davaine, van Beneden, Leuckart, Kuchenmeister. 

 In 1842, Steenstrup had discovered, in certain 

 insects, the alternation of generations; in 1852, 

 Kuchenmeister proved that the generations of 

 internal parasites are similarly alternate. By 

 feeding carnivorous animals with "measly" meat, 

 he produced tapeworms in them ; and by feeding 

 herbivorous animals with the ova of tapeworms, 

 he made their muscles "measly." 



The feeding of animals was the only possible 

 way to understand the bewildering transformations 



