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Park, 1902, inoculated 6 monkeys on the skin with variola virus. All the ani- 
mals yielded a typical pock at the site of inoculation. Both fresh and dried virus 
was found active on the monkey. He found monkeys refractory to inoculation with 
virus from cases of varicella and points out the value of such a test in diagnosis 
of obscure cases where a differential diagnosis must be made between variola and 
varicella. This author considers “Java” monkeys most suitable for the test. 
Blaxall and Fremlin, 1903, show that by feeding monkeys with vaccine virus 
mixed with their food, specific lesions may result in the mouth (one case), or the 
mesenteric lymph nodes (one case) may become a locus of the virus. Their 
results were controlled by inoculations on the calf. 
Magrath and Brinckerhoff, 1904, found ‘“Macacus” and “Rhesus” monkeys to 
be susceptible to inoculation with variola virus. They call attention to the fact 
that the disease produced is related to variola inoculata in man rather than to 
variola vera and that the specific lesions produced in these monkeys contain 
Cytoryctes variole. In a second paper the minute study of the specific lesions 
is presented and it is shown that both the cytoplasmic and the nuclear forms of 
the parasite are present. 
Magrath and Brinckerhoff, 1903, in studying the blood of variolated and 
normal monkeys found a variety of bodies which they interpreted as derivatives of 
the blood cells of the animal. 
The difficulty of getting monkeys in those places where the bulk of 
scientific work is carried on explains the scanty data to be found in the 
literature upon the reactions of this animal in variola and vaccinia. As 
the foregoing summary shows, the only worker who had animals enough 
to do adequate controls and to inoculate a sufficient number for the solu- 
tion of his problems was De Haan, who worked in Java, where monkeys 
were abundant. In spite of the comparatively small number of experi- 
ments recorded by other investigators, it seems worth while to combine 
the data in the following summary. 
That the monkey is susceptible to vaccinia or to variola has been the 
experience of all students of the subject. In some cases the species of 
monkey used is known, and we find that Macacus cynomologus is sus- 
ceptible to variola and to vaccinia (De Haan), Cercopithecus mona and 
Cebus apella are susceptible to vaccinia (Reed). “Rhcesus’” monkeys 
were successfully inoculated with vaccine virus by Copeman and by Reed, 
and with variola virus by Copeman, by Ewing, and by Magrath and 
Brinckerhoff. 
“Macacus” monkeys were found susceptible to variola virus by Béclére, 
Chambon, and Menard, by Roger and Weil, and by Magrath and Brincker- 
hoff. An “African” monkey (Ewing), “Java” monkeys (Park), and a 
“Cercopithecus” (Zulzer) have also been shown to react to inoculation 
with variola virus. It is unfortunate that the species of monkey used 
by various investigators is not known, as it may be possible, from state- 
ments made in the literature, that different species of monkeys may 
present different degrees of susceptibility both to the contagium of 
variola and to that of vaccinia. 
The acme of the process at the site of inoculation in vaccination is 
placed by Copeman at the eighth day of the disease. De Haan finds it 
