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in time to prevent the occurrence of further cases. Of these
3 cases 1 was an unvaccinated child and 2 were adults
vaccinated in infancy only. I may here mention that 7 of the
notified cases of chicken pox were over 15 years of age; 2 of
these were afterwards found to be small-pox, but I have no
doubt that the remaining 5 were genuine varicella; their ages
were 15, 22, 26, 35 and 38 respectively. It appears then
that whereas 98 per cent. of the chicken-pox cases were under
15 years, this disease certainly does occur at a much
higher age.
7. Difficulties of Diagnosis. A well marked case of smallpox
is very easily recognised after the rash has developed, but
in vaccinated persons many cases are so mild or otherwise
modified that the greatest difficulty is experienced in arriving
at an early decision, which must precede isolation.
Most doubtful cases come under two heads:—
(1) Those in which the symptoms are so little marked
that no certain diagnosis can be made;
(2) Those in which the rash closely resembles that of
Chicken pox.
I have observed 8 cases in which fever without rash occurred
about 12 days after exposure to Small-pox. I believe this
fever was the expression of an abortive attack of Small-pox.
All these cases had been successfully vaccinated more
than three days after exposure to Small-pox. In 2 cases
vaccinated five days after exposure, one had a mild febrile
attack and no spots, and the other at the same time a few
typical Small-pox spots and no fever. I did not consider that
in any of these cases the vaccination was itself the source of
the fever. Fortunately there seems no reason to think that
these cases are infectious. The difficulty of distinguishing