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DISCUSSION. 
The experiments detailed above were devised to produce variola vera 
in the monkey or in the orang-utan. An analysis of the results of 
these experiments shows that of 29 monkeys 10 developed a distinct group 
of symptoms. Seven of the remaining animals showed no symptoms 
and 12 were affected in an indefinite way. All the positive results were 
obtained where some product of the cutaneous lesion of human smallpox 
was introduced into the animal. All of the negative results were in ex- 
periments where smallpox fomites or the air of a smallpox ward was de- 
pended upon to carry the contagium. Fifteen experiments in which 
vesicle contents or pustule contents were either inoculated upon the 
tracheal mucous membrane or blown into the lung yielded 10 positive 
results. The disease produced in these animals was characterized by the 
development of an exanthem, some degree of constitutional reaction, and 
fever. The evolution of the exanthem was usually similar to that seen 
in variola inoculata, but in 3 animals it resembled the eruption in a mild 
variola vera. The exanthem appeared between the seventh and tenth days 
of the experiment. The constitutional reaction and the fever appeared 
on the sixth, seventh, or eighth day of the experiment. 
The disease which occurred in these animals agrees with that type 
which follows variolation of the skin of the monkey, and we have no dif- 
ficulty in recognizing it as variola imoculata. 
The negative results which followed exposure of the monkey and the 
orang-utan to smallpox fomites and smallpox patients show that these 
animals do not develop a recognizable form of variola when placed under 
conditions which we believe would produce smallpox in man. We are 
unable to exclude the possibility of the occurrence of variola vera sine 
eaanthem or variola inoculata sine exanthem in these animals. The 2 
monkeys which were refractory to variolation after exposure to a small- 
pox patient might owe their immunity to such unrecognizable forms of 
variola, but we are inclined to regard this phenomenon as very likely due 
to an individual peculiarity of the animals (natural immunity). 
The histological study of the tissues from these series of monkeys 
brings out certain points of interest. The epithelium of the trachea is 
shown to be capable of harboring the parasite of the disease, and we see 
that a lesion can develop in this location which has features in common 
with the ones produced by variolation of other mucous membranes. 
The occurrence of a variolous lesion in the bronchus and, associated 
with it, a pneumonia in which the parasite is present shows that the 
organism is capable of multiplying in the deeper parts of the respiratory 
tract. This fact bears upon the pathogenesis of variola vera in man. It 
is quite conceivable that such a lesion might run its course unnoticed 
and serve as a focus for the multiplication of the organism during the 
incubation period of the disease. We have shown that Cytoryctes 
variole is capable of infecting the endothelial cells of capillaries and 
