Contagious Diseases of Insects. 285 



an ice-house, thus pushing the feeding season out of the 

 natural time and subjecting the worms to unfavorable summer 

 heat, or providing them with leaves too far advanced towards 

 maturity. This might, indeed, seem plausible had not several 

 other lots, fed in the vicinity, but not so retarded, died in the 

 same way. It is interesting to note that in some of these small 

 and isolated experiments in silkworm feeding, certain lots from 

 the same kind of eggs as our own, produced from the same lot 

 of moths, fed on the same kind of food, remained perfectly 

 healthy and produced good cocoons, while others totally failed. 

 It seemed that in every case where what appeared to be the 

 disease called in this paper fincherie became once introduced, 

 few or none of the worms lived to spin passably good cocoons. 

 Most of them died after the third or fourth moults, and after, 

 therefore, no little care had been bestowed upon them." 



My own observations on this phase of the subject were of 

 an experimental character, and will be found in detail under the 

 head of Experiments for Artificial Infection. Here I need 

 only say that they demonstrated the possibility of affecting with 

 disease healthy larvae of the common cabbage butterfly ( Pieris 

 rapip) by means of artificial cultures of the bacteria occurring 

 in the sick silkworms, — these cultures being made in beef broth 

 and applied to. the cabbage worms in confinement by sprinkling 

 or spraying their food. 



Artificial Cultures. 



Our first cultures of the bacteria of the silkworm were 

 made July 30, in test tubes of beef broth, by the methods 

 described above, in my account of the cabbage worm disease, 

 the material for infection having been obtained from a yellow- 

 skinned larva (affected by jaundice^ received on the same date 

 from Professor Burrill, of Champaign. The larva used was 

 recently dead, but still perfectly fresh. Two cultures were 

 made, one from the blood and one from the alimentary fluids. 

 Xo bacteria were discernible in the blood, either in fresh 

 preparations or in mounted films, the latter presenting only 

 numerous and excellent examples of the mulberry cells and 

 granules characteristic of the disease. The slides prepared from 

 the fluids of the alimentary canal, however, exhibit numerous 



