Bacterial Disease of the Squash-bug. 367 



This record seems to indicate that there is no deterio- 

 ration in the properties of this organism when grown 

 successively on agar cultures. The individual variations 

 in the above table are probably due entirely to a differ- 

 ence in the resistance of the bugs themselves. 



Chemical analyses of the pathogenic principle produced 

 by this bacillus have been kindly undertaken by Profess- 

 ors A. W. Palmer and H. S. Grindley, of the University 

 of Illinois. 



MICROSCOPIC CHARACTERS. 



Slides of this organism direct from the insect, if prop- 

 erh' stained, show a short bacillus, single or in pairs, 

 usually 1.2-1.8yuX0.6-0.8yw. The young baciUi are usu- 

 ally homogeneously stained, but the adult and dividing 

 cells often stain more densely at the poles, frequently 

 leaving the middle part entirely clear (see Plate XXYII., 

 Fig 1). Every gradation from one to the other occurs 

 abundantly in a .'-ingle preparation. This so-called belted 

 appearance of many bacteria has been written about 

 at length and speculated upon by Billings* and others. 

 In this bacillus the appearance is often less truly 

 belted than the figures of Billings would indicate for the 

 germ of hog cholera, and the line of demarcation be- 

 tween the stained and the unstained portion is less 

 marked. With a magnification of about five hundred 

 diameters, this unstained portion has much the appear- 

 ance of highly refractive spores; but higher magnifica- 

 tions easily demonstrate the true nature of these condi- 

 tions. As far as I have observed, the belted appearance 

 does not appear in preparations made from cultures; 

 and in the latter the rods are uniformly shorter. The 

 organism as obtained from agar cultures stains well in 

 acid fuchsin and in Hoffmann's violet. Slides direct from 

 the insect give excellent results with a, glycerine solution 

 of violet anilinet, the only difficulty with the latter 

 being that the preparations fade with age, 



*" Swine Plague, its Cniisi'S, Nature, and Prevention." (Bull. Neb. Agr. F.xper. 

 Station, Vol. 2, Pt. I., p. 104, etc.) 



+For this stain, and for various tochnical su<;v;estions, I am indebted to Professor 

 T. J. Burrill. 



