Jxiii.J Causal connection with infectious disease. 147 



the task was comparatively easy in the vegetable kingdom, partly 

 because the structure of plants makes them more accessible to 

 research, partly because most of the parasites which infect them 

 are true Fungi, and considerably larger than most of the con- 

 tagia of animal bodies. 



From this time observers in the domain of animal pathology, 

 partly influenced, more or less, by these discoveries in botany, 

 and partly in consequence of the revival of the vitalistic theory 

 of fermentation by Pasteur about the year i860, returned to 

 Henle's vitalistic theory of contagion. Henle himself, in the 

 exposition of his views, had already indicated the points of 

 comparison between his own theory and the theory of fermenta- 

 tion founded at that time by Cagniard-Latour and Schwann. 



Under the influence, as he expressly says, of Pasteur's 

 writings, Davaine recalled to mind the little rods iirst seen by 

 his teacher, Rayer, in the blood of an animal suffering from 

 anthrax, and actually discovered in them the exciting cause of 

 the disease, which may be taken as a type of an infectious 

 disease both contagious and miasmatic also, in so far as it 

 originates, as has been said, in anthrax-districts. This was, in 

 1863, a very important confirmation of Henle's theory, inasmuch 

 as a very small parasite, not very easy of observation at that 

 time, was recognised as a contagium. It was some time before 

 much further advance was made. Rather the too great zeal of 

 inexperienced observers, especially excited by the cholera-epi- 

 demic of 1866, led to a so-called searching for parasites, barren 

 of all but mischievous results, which was the more calculated to 

 repel more earnest observers because for a time it attracted 

 some measure of applause. These are things which are now 

 long passed away and require no further notice. 



Since about the year 1870 more general attention has been 

 again directed to these questions. The number of publications 

 discussing or bearing upon them is rapidly increasing, and we 

 cannot follow them here in detail. Prominent among them, as 

 new and especially suggestive attempts to deal with the subject, 



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