14a ee ee 
PART V. 
ON THE REACTION OF VARIOLA VIRUS TO CERTAIN 
EXTERNAL CONDITIONS. 
Introduction.—In the experiments described in the other parts of 
this report we have been engaged with the reactions of the inoculated 
animal to the contagium of smallpox and of vaccinia. In this section 
we propose to emphasize the changes which the contagium itself under- 
- goes under certain experimental conditions. 
The contagium of variola is demonstrable in the specific skin lesions 
of human smallpox and in the lesions produced in various animals by 
inoculation with such material. The proof of the presence of the con- 
tagium depends upon the results of the inoculation of a suitable animal 
with the suspected material, as no cultural or micro-chemical technique 
has been devised which permits of the certain identification of the 
organism, save in sections of the specific lesion. This being the case, 
we have only limited criteria for estimating the quality of a given sample 
of virus. By inoculation of the monkey we can determine whether or 
not the virus will produce the typical variolus lesion, and if it does do: 
so, we can classify the lesions produced by different strains of virus 
according to the course of development of the primary lesion, the 
occurrence and extent of the exanthem, and the degree of constitutional 
reaction. From these data we may draw certain inferences as to the 
quality of the samples of virus tested. We give below the results of 
such tests of various samples of virus which had been treated in such 
wise as to modify their properties. 
(a) The effect of keeping upon variola virus.—No. 71. A sample of virus col- 
lected from a case of smallpox, at autopsy, in the pustular stage, produced a 
positive reaction when inoculated on the abdomen of a monkey (M. cynomologus) . 
The virus was placed in an ice box where it was exposed to a varying temperature, 
which at times reached many degrees above freezing. Fifty-seven days later the 
virus was found to have a putrid odor. Inoculations on the abdomen of a mon- 
key and on the cornea of a rabbit yielded no reaction of any sort. 
Another sample of virus became putrid after a few days keeping, yet yielded 
typical takes when inoculated on the monkey’s skin. On many occasions vesicle 
contents, sealed in capillary tubes and kept on ice, was found potent after three 
weeks. 
No. 44. Variola disks collected from cases of the epidemic in Boston during 
February, 1902, were tested sixteen months later. The material had been 
subjected to the high temperature of the steamer’s hold during the journey across 
the Pacific. Inoculations on the monkey’s skin and on the rabbit’s cornea were 
negative. 
341 
