Contagious Diseases of Insects. 287 



explanation ; nor did any of those noticed seem to be spore- 

 bearing. The impurity of this culture makes the supposition 

 plausible that some of the bacteria of the orignal infection 

 were introduced by accident and not derived from the silk- 

 worm. The check tube, however, remained unaltered, as usual; 

 and it seems to me more likely that the originals of all these 

 forms were really derived from the alimentary canal. It is not 

 to be supposed that the alimentary contents of a larva long 

 diseased, and, indeed, actually dead, should remain wholly free 

 from invasion by bacteria other than those strictly characteris- 

 tic of its disease. 



The cultivation of bacteria from the blood, although none 

 were microscopically demonstrable in the latter itself, seems to 

 me not a remarkable phenomenon (especially as the fluid was 

 derived from a dead larva), since it could scarcely be credible 

 that the circulatory fluids should, under such circumstances, 

 be entirely free from the peculiar germs of the disease to which 

 the larva had succumbed. It must be remembered that a single 

 individual Micrococcus would be sufficient to start the culture 

 in the tube, and that the quantity introduced into the beef 

 broth was much greater than that represented by the films 

 microscopically examined. Furthermore, an occasional Micro- 

 coccus in a stained film may readily be overlooked or passed as 

 doubtful, since the difficulty of distinguishing single individuals 

 from accidental granulations of the film itself forbids positive 

 identification of the micrococci unless they occur in numbers 

 sufficient to make their character unmistakable. 



Another culture, commenced July 30, from the silkworm 

 4603, the bacteria from which were described under this number 

 on page 281, was examined August 1, at which time the fluid 

 was observed to be milky and found swarming with micrococci 

 and a few examples of Bacterium (?). (The latter, it will 

 be remembered, were also observed in the original material.) 

 The resultant culture was possibly impure, the two forms appear- 

 ing on the slides being distinguished, however, only by the posi- 

 tive strong stain of one and the very delicate stain of the other, 

 shapes and sizes not being appreciably differenl .* That distinctly 



*Those lightly stained were probably the empty walls of dead 

 examples. 



