40 TRANSACTIONS OF THE ILLINOIS 



kept in a separate cage as a check lot, and fed with leaves brushed 

 with distilled water, had died of schlafEsucht. and the disease also 

 appeared among other larvae in the laljoratory. showing that it had 

 either escaped from our control, or else had developed spontaneously 

 —in either case making further experiment valueless. As a result, 

 therefore, of this experiment, we can only say that seven of ten 

 infected larvae were attacked by schlali'sucht, and only one of those 

 not infected. 



Putting now all these facts together, — the result of the studies 

 of Pasteur on schlaffsucht of the silk-worm, the evident identity of 

 this disease with that of the cabbage-worm and of the other cater- 

 pillars experimented upon, the indications I have given of the con- 

 tagious character of the cabbage-worm disease as shown by the 

 experiments of Prof. Osborne and Dr. Boardman, the readiness with 

 which its germs may be artificially cultivated^ and the reproduction 

 of the disease in apparently healthy insects by treating their food 

 with fluids containing these germs, — I believe that we have fair 

 grounds for at least a reasonable hope that out of all this we may 

 bring an important addition to our means of defence against inju- 

 rious insects. 



I have now under way experiments which will show the length 

 of life of these germs, — that is, the time for which they may be 

 kept either alive or in a condition of latent activity. There is every 

 reason to suppose that they may be preserved from season to season, as 

 the very similar virus of cow-pox is frequently kept for vaccination; 

 but we must test this matter exactly. From such preserved material 

 it will be easy to start new cultures next year, and to experiment 

 with it on a larger scale. A fruit jar of fresh beef broth, for exam- 

 ple, may, next summer, be infected with the contents of one of my 

 sealed tubes, or with a little portion of one of my dried films, and 

 afterwards sealed as when fruit is canned. If the germs these con- 

 tain are then living, the beef broth will, in a day or two, become 

 milky with untold myriads of the rapidly multiplying niicrococc, and 

 a quart of this fluid poured into a barrel of water would doubtless 

 furnish a virus of sufficient strength to inoculate effectually a mul- 

 titude of insects with the disease. 



Of course a great deal of difficult work remains to be done 

 before we can talk with much confidence on this matter. I did not 

 promise to drain our entomological swamp to-night, but only to out- 

 line apian for its drainage; and I shall have accomplished the greater 

 part of my present purpose, if I have given you a clear idea of the 

 class of subjects, and the kind of work upon them, from which I 

 believe that we have the most to expect for the future of economic 

 entomology. 



Without forgetting the things which are behind, let us press on 

 to the things which are before; without neglecting the current sub- 

 jects and methods of the economic entomologist, I believe that we 



