126 Proceedings of Royal Society of Edinburgh. [sess. 
as indeed in all the others — a careful record is kept by which the 
identity of the operator is known and any shortcoming on his part 
brought home to him. After decanting, the empty flasks and 
syphons are sent to the cleaning department, while the batch of 
bottles is labelled with date and number of flask from which they 
are taken. These bottles are kept separate for ten days, and then 
from each batch two samples are taken at random for examination. 
These are opened and a drop from each is placed (fig. 6) in a couple 
of test tubes containing 10 c.c. of sterile bouillon. If after four days 
of incubation no sign of growth is apparent, the batch to which it 
refers is passed into the packing department. Two standard bottles 
from each brew are sent up to the Superintendent to have the dose 
fixed. This is at present done by estimating the opacity of a 
layer of constant thickness, and the results are checked occasionally 
by actual experiment on human beings. This may not appear a 
scientific procedure, but it has proved in practice surprisingly 
accurate, and no other workable method has as yet been devised, 
though many have been tried. 
Inoculation of animals has hitherto proved unreliable for this 
purpose, and even if effective would be unmanageable on the scale 
on which we work. For instance, it is quite usual for the laboratory 
to turn out twenty-five different brews in a day for weeks on end, 
each of which would, if tested on animals, require the sacrifice 
of three lives, or a total of seventy-five animals daily. This would 
necessitate the employment of two or perhaps three skilled bac- 
teriologists devoting their whole time to this and nothing else, to 
say nothing of the number of assistants and animal keepers, and 
the multitude of animals that would be required. The dose having 
been fixed, the labels can now be filled up for each bottle. Another 
long label with directions for opening and handling is pasted 
across the stopper to preserve the contents from the investigations 
of the curious. The bottles are then packed in pairs in wrappings 
of corrugated paper and stowed in boxes holding 1000 doses, for 
transmission to any part of the world. To give an idea of the 
care with which these various processes are carried out, I would refer 
to the number of tests the material is subjected to at every stage 
of its manufacture. The elaborate precautions taken to ensure the 
purity of the microbial growth to begin with, the daily supervision 
of the fermenting flasks, the trial for purity before the sterilisation 
