Contagious Diseases of Insects. 281 



tents of the greater number had been converted into very 

 distinct pale granules, varying in size in the different cells from 

 2 p in diameter to 4 ^ or 5 /*. About 20 or 25 of the larger size 

 were usually contained in a single cell, and a multitude too 

 numerous to count -of the smaller ones. Here and there in 

 the area of the object were large irregular lacunae evidently 

 filled with liquid fat, as shown by the slightly crystalline 

 character of their contents. 



Whatever we may assume with respect to the bacteria 

 infesting these worms as a cause of the premature pupal degen- 

 eration, I do not know that we have any reason to suppose that 

 they are the only possible cause of such a catastrophe to the 

 insect. Other influences tending to disturb seriously the 

 balance of functions at the critical period when larval life is 

 about to terminate in pupation might not impossibly have 

 the same effect. 



Additional details respecting this peculiar catastrophe to 

 maturing larvae will be given further on, under the head of 

 Mamestra picta. 



THE CHARACTERISTIC BACTERIA. 



As an illustration of some of the conditions characteristic 

 of this disease, I give descriptions of well-mounted slides pre- 

 pared from the fluids of one of the larvae received from Prof. 

 Burrill on the 30th July. The larva was dead when exam- 

 ined, but perfectly fresh. In the blood I found only the mul- 

 berry granules, some free and others still enclosed in their 

 mother cells, as already described, together with blood cor- 

 puscles in various stages of degeneration. My notes at the 

 time and a recent examination of carefully prepared slides 

 show that no bacteria occurred in the blood. 



In slide 4603, material for which was obtained by touching 

 a cover glass to the cut end of a divided worm, I find great 

 numbers of the mulberry granules, varying in size from 2.5 /* 

 or 3 ^ to 6 /*, the more usual diameter being, however, 4.5 p to 

 5 p. With these occurred, everywhere, myriads of micrococci, 

 probably one fifth of the area of the field of the microscope 

 being occupied by them where the film is of moderate thick- 

 ness. These micrococci vary in form from exact spheres, 



