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the 50 cubic centimeters of milk was added 100 cubic centimeters of 
sterile water. The flask was then put into the centrifuge machine and 
centrifuged for one hour at about 2,000 revolutions per minute. The 
milk was diluted with twice its volume of water with the idea that 
it would decrease the specific gravity of the milk and so permit of 
the easier sedimentation of the tubercle bacilli. Usually only one 
animal was inoculated from each sample, though in some cases two 
animals were used. Guinea pigs, largely those raised in the labora- 
tory, of as uniform weight as obtainable, were inoculated with 5 cubic 
centimeters of the sediment of this centrifugalized mixture of milk 
and water. The inoculation was made subcutaneously in the belly 
wall. For each guinea pig a different syringe was used. All of the 
guinea pigs, usually 8, that being the usual number of daily samples, 
inoculated on the same day were kept in the same cage, those that 
remained healthy being controls on their environment, etc. The 
guinea pigs were examined for enlarged glands after about four Aveeks, 
and those with enlarged glands were separated from the others so 
as to avoid the danger of infecting others if the glands broke down. 
Many of the animals inoculated died from acute infection with the 
millions of other bacteria in the milk. Autopsies were made on all 
the animals that died, but no attempt was made to determine the 
causal organisms other than the tubercle bacillus. 
Those guinea pigs which did not die in at least two months were 
chloroformed, after having been tested with tuberculin, and careful 
autopsies were made on each animal. Smears, cultures, and sections 
were made from the various organs of the animals that showed any 
change from the normal. The smears were stained with carbol- 
fuchsin and examined for acid- fast bacilli. Cultures were made on 
glycerinized potato and glycerin- agar. In no instance did any of the 
cultures show a quick-growing acid-fast organism resembling in any 
way Rabinowitch’s butter bacillus. The sections were stained with 
carbol-fuchsin for tubercle bacilli, and also with haemalum and eosine 
for histological appearances. The above details were carried out with 
few exceptions in all of the animals that gave a positive result. 
It occurred to me that those animals which had tuberculosis might 
be differentiated from those with other infections by giving all of 
the guinea pigs alive at the end of two months a sufficient dose of 
tuberculin to cause the death of the tuberculous animals in less than 
twenty-four hours. Several preliminary tests on known tubercular 
animals showed that 2 cubic centimeters of crude tuberculin given 
subcutaneously would almost invariably cause the death of such a 
guinea pig in from six to eighteen hours. As high as 7 cubic centi- 
meters of the same tuberculin given to a healthy pig caused only a 
temporary discomfort, passing off in a few hours. A rather hasty 
