Contagions Diseases of Insects. 319 



blood form. Cultures from the alimentary fluids were never 

 without result, although occasionally impure ; but the com- 

 monest forms there were micrococci like the above, and the 

 next commonest an oval micrococcus of nearly the same size 

 and general appearance. Specimens of Bacillus and Bacterium 

 were frequent in these alimentary cultures, but far less constant 

 than the micrococci. No opportunity offered for experimental 

 infection of healthy larvae of this or other species with the cab- 

 bage worm microbes, either native or cultivated; and conse- 

 quently it must be confessed that, strictly speaking, the proof 

 is incomplete that this affection of the cabbage worm is a germ 

 disease, although it certainly amounts to very strong probable 

 evidence. 



More complete and conclusive studies were made of a dis- 

 ease of the silkworm apparently identical with that known to 

 the French as jaunes, and called jaundice by English and Amer- 

 ican writers. This 'disease, distinguished especially to the eye 

 by the decided yellow color and restless activity of the larvae, 

 by the tender skin, easily broken, and by the free flow of thin 

 yellow blood ; is microscopically characterized by an abundance, 

 in the blood, of the spherical or polygonal granules arid clusters 

 of the same, resulting from the peculiar degeneration of the 

 larval tissues proper to pupation, these being in this case 

 derived chiefly from the fatty bodies and in part also from the 

 blood corpuscles. This disease, therefore, seems to be essen- 

 tially a premature pupal histolysis of the fatty bodies, or, 

 more properly, to be due to a retardation of the pupation of the 

 larva which takes unequal effect on the different tissues, the 

 fatty bodies breaking down before the muscles and membranes 

 are ready for pupal transformation. 



Spherical micrococci .75 ^ to 1 /* in diameter occur in the 

 walls of the alimentary canal as accompaniments of this dis- 

 ease, and are believed to be one, at least, of the exciting causes 

 of it, although it seems not impossible that other retarding 

 influences may produce a similar effect in overthrowing the 

 normal physiological balance as pupation approaches. 



That this supposed jaundice was contagious, was shown 

 by the phenomena of its occurrence at Champaign, and that 

 the bacteria accompanying it were capable of exciting disease 

 in other larvae was proven by first cultivating them repeatedly 



