450 



versity. Besides the usaal polyhedral granules of the disease Forbes 

 found several different forms of bacteria. Various cultures made by 

 him convinced him that a spherical micrococcus, varying in diameter 

 from 0.75 yu to 1 /i is the characteristic bacterium of the disease. He 

 found it i)racticable to cultivate this micrococcus artificially in neutral- 

 ized beef broth by infections from the alimentary canal and from the 

 blood. ^'^ Although the micrococcus itself was not demonstrable in the 

 blood by the microscope, it was obtained therefrom by cultures in 

 which it appeared without admixture of other forms. Intestinal cul- 

 tures were, however, liable to contamination by other bacteria but 

 doubtfully connected with the disease." 



The lateness of the season prevented Professor Forbes from trying 

 infection experiments on silkworms and he was obliged to resort to the 

 cabbage worm. He sprayed broods of these with a beef-broth culture 

 of the spherical micrococcus mentioned above, and although the results 

 were not so definite as desired ''yet they clearly indicated the trans- 

 ference of the disease affecting the silkworm to healthy larvae of the 

 Pieris rapceJ^ He sums up as follows : 



It would have been difficult to establish, by a study of the bacteria alone, any 

 marked difference between the disease resulting from thisexperiment and that native 

 to the cabbage worm, but the symptoms of the two diseases are so unlike as to make 

 it impossible to confound them. The general absence of the peculiar discoloration of 

 the common liacherie of the cabbage worm and of the rapid post-mortem deliques- 

 cence even more characteristic of it leave no doubt as to the actual difference between 

 this induced disease and the spontaneous affection. That the artificial disease was 

 identical with that of the silkworm, differing only in such a degree as was to be ex- 

 pected when attacking such widely different larvae, is rendered probable not only by 

 all the attending circumstances but also by the occurrence in the cabbage worm of 

 the myriads of mulberry granules characteristic of the affection in the silkworm. 

 This fact is especially significant, since, in all our numerous examinations of the native 

 flacherie of the cabbage worm, this condition of the fluids was not once observed. 



If we acknowledge that this single experiment is conclusive evidence 

 of the bacterial origin of the disease we have an easy explanation of 

 the difference of opinion entertained by Europeans as to the cause of 

 the malady. The characteristic bacteria might well exist in the larvae, 

 but under conditions so healthy as to prevent their abnormal develop- 

 ment. The loss of vitality due to improper preparation or care of the 

 eggs, to bad ventilation or a damp atmosphere, to a sudden change 

 in meteorological conditions, or to impaired digestion owing to improper 

 food, might supply in a moment those conditions necessary to the devel- 

 opment of the organism and the appearance of the disease. Such 

 being the facts Haberlandt, in the absence, probably, of the needful 

 micrococcus, failed to induce the grasserie by putting the worms into 

 a cold, damp cellar. Worms raised from eggs laid by moths from an 

 infected brood have died of flaccidity, not grasserie, and attempts to 

 produce contagion by smearing the food with the blood of infected 

 worms have given but negative results. 



