AGf~ICULTURAL RESEARCH, PUSA.

240 PRACTICAL BACTERIOLOGY
sediment and kcpt under observation to ascertain
whether tuberculous lesions result (vide p. 298).
Onc guinea-pig is killed at the end of foul' wecks, and
an autopsy carried out; if it shows no tuberculous
lcsions the other animal is kept for eight weeks, when
it is killed and examincd.
An tllternative method is to ccntrifuge 100 c.c. as aboyc and
suspcnd the deposit in 2'5 C.c. of saline. The resultant emulsion
is injected intramuscularly into the thighs of two guinea-pigs.
'rhe animals are kcpt for five weeks, when both arc killed and
examined.
Lesions should be examincd microscopically for
tubercle bacilli to confirm their tuberculous nature.
(It has been Rhown that B. abortus, which may oc.cur
in cow's milk, produces tubercle-like lesions in guineapigs.)
It is ncccssary to inoculate at least t.wo animals
from one specimen, as inoculated guinea-pig.s may
die sometimcs from infection with other organisms
present in the milk--e.g. sporing anaerobic bacilli. 'rhis
difficulty may he obviated by treating the sediment
with alltiformin (vide p. 302) before injection. Some
intercurrent discase--e.g. pneumonia, enteritis, etc.may
also cause death beforc tuberculous lesions havc
dcveloped and so nullify the test if only one animal
is injected.
Some of the cream from the centrifugalised milk"
may also be uscd for the inoculat.ion.
'rhe microscopic examinatiou Illay reveal acid-fast bacilli
other than the tubcrcle bacillus (vide p. 305). The absence of
tubercle lJUcilli in films does not exclude their presence in the
specimen. The inoculation test, therefore, is thc only valid
mcthocl of dcmon;\trating tubercle bacilli in mille.
Other pathogens in mil/c.-'rhe mcthods for demon­
.st.rating B. typhosus (and B. puratyphosus) and B.
diphlheriae correspond to those used for the isolation
of these organisms. For B. typhOSltS, the sediment,
after ccntrifugalisation, should be plated out on the
surface of MacConkev's medium and at the same time
tubes of brilliant-grecn peptone water are inoculated