ON PARASITES. 7 



simple organism whose onlj members are a few small booklets, is 

 accidentally discovered upon a blade of grass or in a drop of water 

 from a ditch, a cesspool, or stream. Has sucb a defenceless little 

 creature any relation with the formidable tapeworm that devours the 

 sustenance of the unfortunate victim whose intestines it infests ? It 

 was the crowning triumph of German assiduity and skill to establish, 

 the fact. In the interior of the tissues and upon the free mucous 

 surfaces of the human and other organisms, secondary organisms of a 

 low grade of development are found, apparently formed in the locality 

 that they inhabit. Whence do they come, and how do they originate ? 

 The ancients explained them as freaks of nature, creatures of equivo- 

 cal or spontaneous generation, i. e., simple results of the concurrent 

 action of the forces at work in the place where they were developed, 

 upon matter collected there. And even since the new era in embry- 

 ology inaugurated by Eedi and Vallisneri there have been, and still 

 are physiologists who maintain the generatio equivoca of these beings. 

 Thus we quite recently have Beauchier and Viguier gravely declaring 

 that, "in the predisposition to entozoa the thick mucus of the 

 intestine comes under our consideration, in the first place, as being 

 acid itself it cannot purify the blood from acids. From a portion of 

 the mucus the worms are produced with the assistance of astiienia and 

 adynamia by the generatio equivoca. The worms produced are as the 

 analysis shews, still more acid than the mucus from which they are 

 produced. Emetics, drastic purgatives, mercury, antimony and 

 arsenic certainly kill the worms, but weaken the constitution, and 

 thus actually rouse the generatio equivoca into activity, and cause the 

 formation of worms," &c., &c. Of such physiologists we must say 

 scientia non docet. The zealous researches now prosecuted everywhere 

 in the embryology of the lower animals and especially the entozoa, 

 have, however, routed the partizans of the generatio equivoca from 

 their last field of contest, and conclusively established the universal 

 correctness of the doctrine omne vivum ex ovo. 



The metamorphoses and habits of many of these creatures surpass 

 in strangeness those exhibited by inhabitants of the outer world. 

 Although of simple structure and no particular beauty of form to the 

 eye, the microscope invests them with the fairest proportions and a 

 complexity of structure often surpassing that of higher animals. 

 Active investigations are being conducted among these interesting 

 beings, and new species are continually added to those already known, 



