Contagious Diseases of Insects. 265 



The Characteristic Bacteria. 



As implied in the foregoing, I have no doubt that a large 

 percentage, at least, of the minute spherical granules abundant 

 in the fluids of the body and alimentary canal of the diseased 

 larvge are genuine bacteria, belonging to the genus Micro- 

 coccus I cannot hope to convey verbally the same conclusive 

 conviction of this fact which I have myself derived from long 

 study of these little forms under a great variety of conditions, 

 and the preparation and examination of a multitude of slides, 

 both recent, and permanently mounted. These latter were some- 

 times unstained, and again stained with a considerable variety 

 of aniline dyes, — brown, blue, violet, and magenta. Several 

 successful cultures have also assisted to confirm this view, the 

 products of the cultures being unmistakably the form originally 

 taken from the caterpillars under experiment. 



In form the micrococci of the cabbage worm are usually 

 strictly spherical, although in the alimentary canal a patch will 

 occasionally occur in which they are of a slightly oval outline. 

 The micrococci of the fluids of the diseased larvae seen in the 

 field of the microscope are mostly separate spheres, but a con- 

 siderable percentage of them are attached in pairs, as if in pro- 

 cess of division. Rarely a short chain of four, six, or eight 

 may be seen. In the stomach they occur not infrequently in 

 compact patches or zoogloea-like masses. In size the individuals 

 vary from .5 ^ to 1.25 fi in diameter, the small forms being 

 those in the blood and the larger those in the stomach. Indi- 

 vidual larvaj differ, in fact, with respect to the size of their 

 micrococci, in some the average of those found in the blood 

 being not far from .75 ^ tol fi^ while in others they barely reach 

 .5 fi. Commonly, those of the stomach average 1 /t. 



In addition to the direct evidence above adduced, the close 

 resemblance of these corpuscles to those occuring in other 

 larvge affected similarly to the cabbage worm, in which the 

 bacterial character was even less obscure, gave indirect and cu- 

 mulative evidence with respect to the nature of those forms 

 in the cabbage worm. Their reaction to the usual staining 

 fluids was such as the hypothesis of their bacterial character 



