476 Prof. H. J. Detmers on a Pathogenic ScMzophyte. 



from analogy between diseases of animals and plants, Prof. T. 

 J. Burrill *, of the Illinois Industrial University, more 

 favoured by the nature of the objects of his investigation 

 (apple-trees, pear-trees, and peach-trees), has furnished evi- 

 dence, amounting to almost absolute proof, that the so-called 

 blight of apple-trees and pear-trees and the so-called "yellows" 

 of peaches are caused by Schizophytes similar in size (but 

 otherwise not identical) to those which I consider as constitu- 

 ting the cause and infectious principle of Swine-plague, as will 

 be seen by consulting the transactions of the meeting of the 

 American Association for the Advancement of Science in 

 Boston, 1880. 



5. If the infectious principle were a chemical poison or virus, 

 its action, one would suppose, would under all circumstances 

 be exactly the same, and the malignancy of the morbid pro- 

 cess and the time required for its development (the so-called 

 period of incubation, or, more correctly, stage of colonization) 

 Avould not be subject to changes dependent upon the season of 

 the year, upon the individuality and temperature of the ani- 

 mal, and upon other yet unknown external iniluences, as is 

 undoubtedly the case. An organic poison or virus, one would 

 suppose, would act somewhat like the virus of a poisonous 

 snake. In the same localities, in the same places, or the 

 same yards and pens, and among the same breeds of hogs, in 

 which the disease was exceedingly malignant in 1878, it was, 

 as a rule, much milder in 1879, and still milder in 1880. As 

 such are unmistakable facts, repeatedly and everywhere 

 observed, it must be concluded that nothing but what is able 

 to undergo changes, is subject to growth and development, and 

 acquires vigour and propagates rapidly under favourable, but 

 is weakened and multiplies slowly under unfavourable cir- 

 cumstances (in other words, nothing but what is corporeal and 

 endowed with life), can constitute the cause. 



6. If the cause and infectious principle of Swine-plague 

 were a chemical poison or virus, one would suppose a cessa- 

 tion of the morbid process would be impossible, and an animal 

 would never recover while its organism contains an abundance 

 of the infectious principle in an effective condition — as is un- 

 doubtedly the case, because convalescents and animals nearly 

 recovered frequently communicate the disease, even in a fatal 

 form, to other healthy pigs ; further, the fact that an animal 

 once recovered possesses but little predisposition for future 

 infection, or is seldom attacked a second time even if ever so 

 much exposed, and then only contracts the disease in a com- 

 paratively mild form, could never be explained. But the whole 



* ' Science,' vol. i. pp. 162, 191. 



