PART III. 
STUDIES UPON THE IMMUNITY REACTIONS OF THE MON- 
KEY AFTER INOCULATION WITH VACCINE OR WITH 
VARIOLA VIRUS. 
1. ON THE IMMUNITY REACTIONS OF THE MONKEY (MACACUS CYNOMOLOGUS ) 
AFTER INOCULATION OF THE SKIN WITH VACCINE OR WITH VARIOLA 
VIRUS. 
In this section we propose to bring together certain observations upon 
the immunity following the development of vaccinal or variolous lesions 
upon the skin of the monkey. The data bear upon the general problems 
of immunity to vaccinia and variola, and we will show certain differences 
in the immunity reactions of the monkey to the two sorts of virus which 
throw light upon the general question of the interrelationships of the 
two diseases. The experiments which form the basis of this section were 
in part those detailed in other papers of this series and in part the ones 
performed with special reference to the problems here treated. 
The technique used for inoculation was that described in previous 
papers of this series. The diagnosis of the results of the second inocula- 
tions was based upon the descriptions already given of the specific lesions 
of vaccinia and variola inoculata in the monkey. We have been guided 
wholly by the appearances to the naked eye. In our experience we have 
rarely been in doubt as to the specific character of a vaccinal or variolous 
skin lesion in the monkey. In the few instances where we could not 
feel certain of the diagnosis, the experiment has been ruled out. 
EXPERIMENTS. 
1. Vaccination of the skin after successful vaccination of the skin.— 
Thirteen monkeys were selected for this experiment. Each animal had 
shown a typical vaccinal lesion of the skin of the abdomen from inocula- 
tion either with virus No. 1, 148, 236, 246, or 251. Twenty-two days 
after the occurrence of this lesion the animals were vaccinated on the 
skin of the abodmen with virus No. 148. All these attempted revaccina- 
tions resulted negatively. At the site of the second inoculation there 
was only the usual, slight reaction which follows a scratch. The scratches 
healed as if no virus had been used. 
2. Variolation of the skin after successful vaccination of the skin.—Six 
monkeys which had shown typical lesions on the skin of the abdomen as 
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