TEACHING OF RUDOLPHI. 29 



the way of such a theory. The microscope had been for some time 

 laid aside as a not very trustworthy agent, and a simple lens, or the 

 naked eye alone, was sufficient to watch the process of spontaneous 

 generation. 1 When this had once taken place, it was supposed that 

 the Entozoa increased by sexual generation, or else to what purpose 

 had they been provided with generative organs ? The significance 

 of this sexual generation had been kept in the background by the 

 prevailing opinion of spontaneous generation. The majority of the 

 eggs were extruded without being further developed, for, if not, the 

 extraordinary fertility of these creatures would entirely fill their host 

 with their progeny. The supporters of this view, from being well- 

 known authorities in their subject, had such weight, that they readily 

 crushed the evidence advanced against their theory by other observers. 

 This misfortune was partly the fault of their opponents, generally men 

 like Brera, 2 who, in spite of all other qualifications, was ignorant of 

 the necessary details of the subject. As long as Kudolphi's teaching 

 was followed, and the theory of vitality was generally accepted, this 

 view just stated of the origin of the Entozoa was the only one that 

 obtained credence; and it appeared to be strengthened by the discovery 

 of a continually increasing number of bladder-worms and encysted 

 Helminths which were entirely destitute of organs of generation, and 

 were unable, therefore, to propagate themselves by the sexual method. 

 Except by a theory of spontaneous generation, the existence of these 

 worms appeared inexplicable. And yet this appearance was decep- 

 tive so much so, that it is by the help of these very sexless worms 

 that we are now able to show the error of Rudolphi's theory. The 

 general acceptance of this erroneous theory was not, however, over- 

 thrown at a single blow. It was necessary to bring forward numerous 

 facts in order to shatter the belief in spontaneous generation, and set 

 a more credible theory in its place ; but these facts would not have 

 been recognised for a long period, had not a change in the direction 

 and method of biological study given a fresh impulse to helmintho- 



The majority of these fundamental facts were discovered by 

 means of the microscope, which v. Baer, Purkinje, Ehrenberg, and 

 others had again used for scientific investigation, whereby the most 

 brilliant results had already been obtained in other regions of zoology. 

 The first discoveries made by the microscope in helminthology had a 

 most important bearing on the origin of the intestinal worms. 



In the year 1831 Mehlis made the remarkable discovery that the 



1 Bremser, loc. cit., p. 65. Rudolphi, " Entozoorum Hist. Nat. , " vol. i. , p. 811, 1808. 



2 " Medicinisch-praktische Vorlesungen liber Eingeweidewiirmer,' p. 47 ft. seq., 1803. 



