638 FILTERABLE VIRUSES— RICKETTSIA 
acid is without effect. Acids and alkalis, on the contrary, even in low 
concentration, are very injurious. 
Bordet and Ciuca^ state they have obtained an antibody which 
prevents phage activity by injecting rabbits with solutions containing 
the active principle. The antibody is not very potent, however. 
The Nature of Phage.— Twort,^ was not committal in his communica- 
tions. d'Herelle believes the phenomenon is due to an ultramicroscopic 
parasite, and it may be conceded that there is much in common between 
his principle and filterable viruses in general, at least in generic char- 
acteristics. Much point has been made by his opponents, however, 
about the unusual resistance of phage to physical and chemical agents. 
It would appear, however, from a survey of the literature, that the 
opponents of the ultramicrobic theory have elaborated even more 
unusual speculations in their attempt to evade the resistance factor of 
phage. Thus Kabeshima^ believes that phage arises as a catalytic 
agent in the tissues of infected animals: this is supposed to activate a 
preenzyme in the substance of the invading microbe which in turn 
causes its lysis. Bordet and Ciuca"* have suggested that phage may 
originate as a reaction between defensive factors in an infected animal 
and the microbe, which causes a transmissible disturbance of nutritive 
function in the microbe, manifested chiefly by a preponderance of 
autolytic processes which cause the lysis of the microorganism. 
d'Herelle attributed a major part in recovery from microbic infec- 
tion to his Microphagum intestinale and hoped that it might be possible 
to infect animals and man with phage and thus augment materially the 
offensive forces of the body against bacterial infection. Some remark- 
able experiments have been reported,^ but on the whole the results in 
man at least, have been disappointing thus far. It is necessary to wait 
for additional information both upon the nature of phage, and the 
methods for handing it successfully before final judgment can be 
rendered. 
RICKETTSIA BODIES. 
The Rickettsia is a fairly well-defined group of minute, bacterium- 
like bodies, which up to the present time have been found primarily in 
the alimentary tracts of certain insects, and other Arthropoda. The 
status of the group is still quite unsatisfactory. The difficulties 
encountered, not only in identifying them, but also in producing 
unequivocal evidence of their viability, have impelled not a few 
authors to assume the very conservative view that available evidence 
is insufficient to warrant positive statements regarding them. On the 
other hand, the few careful observers that have actually handled and 
studied suitable material are practically unanimous in expressing 
1 Compt. rend. Soc. de biol., 1921, 84, 280. ^ Lq^ pit. 
3 Compt. rend. Soc. de biol., 1920, 83, 219. 
« Ibid., 1920, 83, 1293; 1921, 84, 276, 280, 745, 748; 85, 1095. 
'^ See article, Bacteriophage, Physiol. Rev., 1925, 5, 95, by Bull. 
