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Proceedings of the Royal Society 
and orange, as described by other observers. Secondary cultivations 
were made from certain of the tubes which had been opened for 
microscopic examination. In only one case out of six were the 
same colours reproduced. Change of colour in the growth was thus 
observed to take place both in primary and secondary cultivations. 
It is difficult to explain how this can take place on the supposition 
that we have three different organisms to deal with. 
2. Histological Examination of Vaccine Cultivations. 
A. Orange cultivation showed swarms of minute spherical 
“ micrococci ” without definite arrangement. 
B. White cultivations showed single, double, and triple micro- 
cocci, and in one case a sarcina form. The micrococci were larger 
in cultivations which had been incubated. 
C. Yellow cultivations showed dumb-bell and sarcina form 
micrococci. Here also the incubated cultivations showed larger 
torula-form micrococci. 
We could not explain these different appearances. It was sup- 
posed that we had three different organisms, any one of which 
might be the immediate cause of vaccinia. Other preparations of 
vaccine lymph, clear and opaque, were now made. 
In clear lymph certain minute badly stained spherical bodies 
were recognised similar to those of the orange vaccine cultivation, 
but I am indebted to Dr Francis Troup for the first clear demonstra- 
tion of them in vaccine lymph. I then saw that the “ micrococci” 
in clear lymph and orange “ vaccine ” are identical. Opaque 
lymph after being kept some time showed large spherical trans- 
parent bodies like oil drops, but their nature was a mystery. 
Even after examining vaccine cultivations, we were as far off as 
ever from being able to explain the nature and cause of opacity in 
lymph. I therefore suggested that we should cultivate variola. 
III. Examination of Cultivations of Variolous Lymph. 
As there were no cases of small-pox in Edinburgh suitable for our 
purpose, it became necessary to visit the Hospital Ships at Purfleet, 
on the Thames, to obtain variolous cultivations. I have to acknow- 
ledge the readiness with which Dr Birdwood placed the material at 
his disposal at our service, and also the able assistance given by 
Messrs Bott and Clatworthy, the resident physicians. 
