32 TRANSACTIONS OF THE ILLINOIS 



many a year, and that the task of subduing it is not one of great 

 magnitude, or involving extraordinary expense or delay. 



There is. perhaps, no subject, unless it be the details of the doc- 

 trine of evolution, which is to-day receiving more active, acute, 

 skillful, learned, and thorougli-going scientific investigation than 

 that of the causes, origin and control of contagious disease. It 

 is easy to cite illustrious examples of this fact. The brilliant dis- 

 covery by Koch, of Germany, that consumption is due to a parasitic 

 bacterium, his Bacillus tiiherculosis, a conclusion now so well estab- 

 lished that the treatment of that disease in the army hospitals of the 

 German Empire is based upon it; the equally brilliant, if not equally 

 important, discoveries of Pasteur, that splenic fever of cattle and 

 the charbon of sheep are likewise germ diseases, and that their rav- 

 ages may be almost wholly prevented by inoculation; the triumphant 

 demonstration by the same savant, — an older discovery, but one more 

 important to our subject, — that the pebrine of the silk-worm, and 

 the scarcely less fatal and destructive flacherie of that insect, are also 

 contagious germ diseases, unquestionably caused by the noxious 

 action of bacteria upon otherwise healthy individuals; these are in- 

 stances more or less familiar to all who read. It is in medical circles 

 that this ferment is most actively working; and one can hardly pick 

 up a medical journal in any language, at the present time, without 

 seeing something on the relations of bacteria to disease. Of course 

 the end proposed in all these extensive, laborious, and most difficult 

 researches, is that of prevention or remedy. The problem with 

 which ire have to deal to-night is. however, the reverse of that. The 

 task I have set myself is to throw what light I can, in the bri6f 

 time allowed me, on the contagious diseases of ifisects, and on meth- 

 ods of spreading, intensifying and accelerating such diseases. 



Ill this country, I do not know that* anything of any importance 

 had been done upon this subject, up to about a year ago, when I made a 

 careful preliminary study of an apparent destructive germ disease of 

 the chinch-bug, some account of which is given in my report as 

 State Entomologist for 1882. In Europe, however, a considerable 

 mass of observations has been accumulated, and some careful and 

 conclusive studies and experiments have been made by biologists of 

 world-wide renown. The studies of the diseases of the silk-worm by 

 Pasteur have already been mentioned, and the foul-brood of bees, — 

 a contagious affection of bee larvas, destroying them while yet im- 

 prisoned in the cells of the comb, has also been carefully worked out by 

 several German naturalists. Metschnikoff, an eminent Russian biolo- 

 gist, and the great botanist, De Bary, have made numerous and 

 highly successful experiments directed to the point in which I have 

 sought to interest you; to that of producing disease in healthy in- 

 sects, although both these scientists were engaged on insect diseases 

 produced by fungi much higher in organization than the bacteria 

 with which we have to do this evenin";. 



