AGf~ICULTURAL RESEARCH, PUSA.

184, PllAC'l']CAL BAC'l'ERIOLOGY
left thumb in the way artists support the hand
when painting. The selected colony is then casily
removed without touching the others. Lay the
plate on the bench, withdraw the right hand to
the othcr end of the holder and inoculate the
required medium in the man ncr previously
described.
Plate C'tdtu,/,e JJ:Hcl'oscope
There are on the lllarketlow-power binocular nmgniHers whidl
arc extrcmely useful for examining plate cultures of organisms;
they have a long wo1'ldng distance so that !L colony call be
" picked off" the plate while using the instrument. When
dealing with uacteria forming slllall delimttc colonies, or where
the colonies of the desired organism arc few ill HumiJer, the
low-power binocular is in valuable. A lllagnifieation of ten
(liametcrs is useful for general work, but by interchangeable
eye-pieces and objectives, magnifications from three to thirty
diameters arc available.
eli. By SHAKB CULTURE IN '.rUBES (vide p. 127). 'nlis
nwthod is sometimes used in the separation of
anacl'O Lic () rganisIlls.
;3. By THE USE OF SF.LEC'l'IVE MKDIA.--Such media
as MacCollkey's for the coli-typhoid gronp, HieudonllC's
for the ('holCl'a vibrio, the various tcllurite media for
B. diphtlwriac, etc., have heen devised so that the
lllajority or the organisms othcl' thl\.l\ those COl' whieh
the media. arc used will Hot grow, and plll'e cullnres
ean Huu;· be obtained.
G. By ANIMAL INOCULATION.-Advantage is taken of
the fact that laboratory aninlals are highly susceptiblc
to certain organisms-for example, the Inouse to the
pneumococcus. If a mixture oj' organisms containing
pneumococci-e.g. sputum-be inoculatcd subcutancously
into a mouse, thc animal dies of pneumococcal
septicaemia in twenty-four to thirty-six hours, and
from the heart blood the organism can he obtained in
pure culture. Similarly the tubercle bacillus can be
isolated from contaminating organisms by inoculation
of a guinea-pig. The tubercle bacilli are founel in
pure culture in the resulting lesions.