143 



the germs producing it has reached the point of practical applicability. 

 Let us see, then, to what extent these conditions have been met or are 

 likely to be met by future investigation. 



The investigations of Pasteur upon the p^brine, etc., of silk-worms 

 and the measures recommended by him resulted in restoring the silk 

 industry of France from a state of probable annihilation to a most 

 prosperous condition. The same measures will protect the silk industry 

 of the United States if it ever assumes important proportions, while 

 there can be little doubt that measures equally effective must result 

 from a knowledge of the foul brood of bees.* From this side, therefore, 

 we can be assured of practical advantage from the studies of insect 

 diseases. As regards the control of these diseases in the other direc- 

 tion there appears to be more difficulty. The disease appears, for in- 

 stance, in a brood of insects that is present in great abundance and 

 kills them off at a tremendous rate, until, perhaps, there is no material 

 for it to feed upon, and it is checked by the destruction itself has 

 wrought. How, then, shall the germ be preserved to start anew in 

 subsequent years? Or the disease may be raging furiously on certain 

 insects in one locality, while healthy insects in countless numbers may 

 be causing their usual havoc in another. How shall the disease be 

 transported and how can it be so spread as to quickly affect the in- 

 sects ? 



To show how these conditions occur in practice I may be allowed to 

 repeat briefly an actual trial in the direction of introduction of one 

 form of disease. During the fall of 1883 I learned that the cabbage- 

 worm disease was raging in Illinois, while at the same time healthy 

 worms were plenty here, there being no evidence of disease. I at once 

 wrote to Professor Forbes, asking him to send me some of the diseased 

 worms. He did so, and in due time they arrived, and I at once placed 

 some of the diseased worms on cabbage plants infested with worms, 

 and also sprinkled some of the plants with water in which I had mixed 

 fluids from the bodies of dead worms. Later I found oue dead worm, 

 apparently from effects of the disease. The cabbages being gathered 

 sooner than I expected put an end to the trial out of doors, but I fed 

 some worms in confinement upon cabbage leaves and exposetl them to 

 the disease. A number of these died with all the characteristics of the 

 disease, and microscopic examinations showed them to contain the same 

 micrococcus as recognized by Professor Forbes to be the specific form 

 of this disease. Last fall, however, the disease commenced at a point 

 very near where I started the experiment two years before, and spread 

 rapidly until, during the latter part of the fall, cabbage worms all over 

 the neighborhood were dying rapidly from its eflects. 



While it is unsafe to affirm that this resulted from the introduction 

 two years previously, It is not improbable that such is the fact, and I 



* A point which is now considered as fully reached. 



