164 TWO NEW INSTRUMENTS FOR BIOLOGISTS, 



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be certain that the eggs or larva? recovered are identical with 

 those administered, and this alone is a serious drawback. With 

 man himself the case stands most precarious. To show this it will 

 suffice to cite one of the best known and most decisive experi- 

 ments of the kind under consideration. Prof. Rudolph Leuckart, 

 the celebrated Leipzig naturalist, swallowed a number of the 

 eggs of Oxyuris vermicularis, the common pinworm or thread- 

 worm of man. About two weeks later he passed some nearly 

 matux'e worms of that species, as it seems did also several of his 

 pupils, who performed the same experiment simultaneously with 

 him. The pei'fectly obvious conclusion is that the worms noticed 

 were those resulting from the eggs wittingly swallowed two 

 weeks previously, providing the experimenters were previously 

 free from Oxyuris. But the proviso seriously mars the result. 

 The more familiar one is with the abundance of the eggs of 

 Oxyuris vermicularis, and the multitudinous chances they have 

 unbeknown to him of getting into the alimentary canal of man, 

 the more one will hesitate in admitting that more than a proba- 

 bility was established by Leuckart's experiments. No one could 

 be better aware of this than the renowned author of the 

 " Parasites of Man," and liis statements ai-e therefore only those 

 justified by his experiments. Succeeding authors have not been 

 correspondingly careful, and one may find the statement in what 

 seem to be authoritative places boldly made on this very evi- 

 dence, that the direct development of Oxyuris vermicularis has 

 now become certain. Balfour very properly qualifies the 

 " certain " by prefixing " almost." 



The suction-capsule will, I hope, lead to a greater amount of 

 certainty in this field. 



The idea embodied in the suction-capsule occurred to me two 

 years ago at Jena. At that time I made some experiments with it, 

 but they came to no satisfactory conclusion as the sequel will show. 

 Recently while making some researches into the life-history of 

 certain Australian entozoa I tried it again and this time with 

 most gratifying results. 



