16 



badly infested forest of 10 acres or more the average number 

 of caterpillars to be collected was placed at less than 50 speci- 

 mens per acre, since the disease spreads best in such localities. 



The local superintendents had been instructed to feed the 

 collected caterpillars daily with oak leaves, or with apple leaves 

 M'here oak leaves could not be secured. These leaves were 

 not to be removed from the twigs, and were to be placed m 

 water for at least four days before feeding. A special em- 

 phasis was laid on not giving as food leaves of trees which had 

 been sprayed with arsenate of lead. As breeding cages com- 

 mon wooden boxes were used, to which the entry of air was 

 provided for by means of gauze coverings. Further, the local 

 superintendents, who were not familiar with the wilt, were 

 taught the character of this disease and its manner of appear- 

 ance, and were instructed to communicate with me at once on 

 the first appearance of Macherie in their breeding cages. The 

 local superintendents were asked to attend to this part of the 

 work, since at that time it was not convenient to rear several 

 thousand gypsy moth caterpillars in one place, and also in 

 order that their interest might be awakened in the experiments. 



As soon as the wilt was determined to be present in a brood 

 the whole material was transplanted upon the previously chosen 

 places, with the help of the respective superintendents. This 

 was done as follows : a piece of clean cloth, burlap, for instance, 

 about 2 feet long by 1 foot wide, was hung in dense foliage 

 between the limbs of a tree, or from one tree to another close 

 by (Pig. 1). In this hammock-like bag were placed, besides 

 the dead and stiU living caterpillars of the brood, also all food 

 remaining in the breeding cage, since such remains might also 

 be supposed to contain organisms of the disease. !N"o means 

 were used to prevent the escape of the sick but still crawling 

 caterpillars, in order that they might disseminate the organ- 

 isms.^ Where possible, the bag with the material was hung 

 about 6 feet or still higher from the ground, in order that the 

 wind might aid in the spread of the disease. In planting 

 the diseased material the direction of the prevailing wind of the 



^ That this is the case is proved by some experimenta which I shall consider particularly later, 

 where only sick caterpillars were transplanted, but no dead caterpillars. 



