Contagions Diseases of Insects. 289 



rod-like form or double elongate oval, the paler centers com- 

 mencing to appear in the oval and becoming more conspicuous 

 as this elongates. 



A single somewhat later culture, commenced August 4, did 

 not differ materially in results from those preceding. No 

 bacteria were discoverable in the blood of the larva, used by 

 prolonged and careful search, but the alimentary fluid contained 

 the usual Micrococcus. Five days later the infected infusion 

 was decidedly turbid, but without either film or sediment. 

 Besides an occasional short Bacillus in active movement, it con- 

 tained only the spherical Micrococcus of the usual size. 



The slides of these various cultures clearly demonstrate the 

 presence of a spherical Micrococcus, varying in diameter from 

 .75 jtt to 1 |tt, as the characteristic Bacterium of the disease from 

 which these silkworms were perishing, and likewise the prac- 

 ticability of artificially cultivating this Micrococcus in neutral- 

 ized beef broth by infections from the alimentary canal and 

 from the blood. Although the Micrococcus itself was not 

 demonstrable in the blood by the microscope, it was obtained 

 therefrom by cultures in which it appeared without admixture 

 of other forms. Intestinal cultures were, however, liable to 

 contamination by other bacteria but doubtfully connected with 

 the disease, among which was the form last described. 



Infection Experiments. 



I found it by no means easy to provide means for testing 

 satisfactorily the possibility of conveying the disease of the silk- 

 worm above described to other demonstrably healthy insects. 

 The late period of the occurrence of the disease under my obser- 

 vation made it impossible to use other lots of the silkworm 

 itself in the experiment, and no other lepidopterous larva 

 was sufficiently abundant at the time, except the cabbage 

 worm. This, however, had alread been found, the previous 

 year, to suffer extensively from an extremely destructive dis- 

 ease of its own, and although at the time the experimental 

 stage of my studies of the sick silkworms had been reached, no 

 evidence of disease among the cabbage worms had yet appeared 

 in the fields^ I had every reason to anticipate its outbreak among 

 them, — a fact which made me very doubtful of really bringing 



