1908-9.] The Pathogenesis of Micrococcus melitensis. 
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XXXIV. — The Pathogenesis of Micrococcus melitensis. By J. Eyre, 
M.D., Bacteriologist to Guy’s Hospital, Member Advisory Board 
of Mediterranean Fever Commission, and Chairman of the 1906 
Working Party in Malta. 
(MS. received February 26, 1909. Read May 3, 1909.) 
Virulence of M. melitensis. 
M. melitensis is virulent to a greater or less degree for all the usual 
laboratory animals — guinea-pigs, rabbits, rats, mice, dogs, and monkeys — 
and by means of suitable passages its virulence for any particular species 
can be considerably exalted. 
Bruce’s early experiments were carried out upon the monkey, in which 
animal he was able, even when using comparatively small doses, to reproduce 
the clinical thermometric symptoms of M. melitensis septicsemia, previously 
observed in man. The virulence naturally possessed by M. melitensis for 
rodents is, however, exceedingly low, and in order to produce a fatal infection 
in these animals it is necessary to introduce enormous doses of a recently 
isolated strain subcutaneously or intraperitoneally : even then the infection 
follows such a protracted course that weeks or even months may elapse 
before death takes place — a fact which sufficiently explains Bruce’s remarks 
in the Practitioner , 1888, vol. xl. pp. 241-9. Speaking of guinea-pigs 
which he had inoculated subcutaneously, he says : “ After keeping them for 
two months I could perceive no difference in their general condition, so 
consider them refractory to the disease.” A few years later (Annates de 
Vlnstitut Pasteur , 1893, vol. vii. pp. 289-304) Bruce further states: “ One 
only obtains negative results on inoculating small quantities of pure culture 
of this micrococcus (melitensis) under the skin of mice, guinea-pigs, and 
rabbits.” Hughes merely repeats Bruce’s conclusions. Babes, too (Hand- 
buck fur path. Alik.), was unable to obtain any evidence of pathogenic action 
on rodents. This was not surprising, as he was working with a strain of 
the coccus obtained from Krai, probably much attenuated from long sojourn 
in the laboratory. 
Attenuation of Virulence. 
Artificial cultivations of M. melitensis, especially when kept at room 
temperature (18-22° C.), undergo a progressive but exceedingly slow 
