ABSTRACTS
69
The vaccine was diluted considerably with physiological salt solution before use, and
injected subcutaneously, divided between various sites. Samples of sera were taken
from the calves after the vaccination and titrated on guinea pigs against foot-and-mouth
virus with a view to ascertain the degree of immunity acquired (but this did not give
clear cut positive results in most instances, except that generalisation was delayed in
some vaccinated cases). After an interval of about three weeks after the second vacci-
nation, the calves were tested for immunity by being placed in contact with an arti-
ficially infected calf along with a healthy calf for control. If the healthy control calf
contracted foot-and-mouth disease and the vaccinated calf remained unattacked, this
was taken as evidence of acquired immunity. This was confirmed, in each such case,
by submitting the vaccinated calf after an interval of two to three weeks to a further
" tongue-test " by inoculation of virus directly into the mucosa of the tongue and upper
jaw. As the " Riems O " and " Virus 2 " strains proved to be of insufficient virulence
for calves, it was necessary to repeat the immunity tests of calves vaccinated with these
strains, against the " Hansen-Fionie " strain which was virulent for bovines.
Three types of material were used as the base for the production of the vaccine
(i) culture fluid, (ii) extract of aphthous membranes, and (iii) lymph.
(i) Culture fluid vaccine.—Culture was effected according to Frenkel's technique.
The ingredients were used in the proportion of five parts of virus, five parts of tissue,
twenty parts of bovine serum and about two parts of phosphate buffer solution. The
tissue and virus were first mixed and allowed to remain in the refrigerator for at least
one hour. The other ingredients were then added and incubated for four days. The
tissue was then removed and emulsified with quartz sand and phosphate buffer solu-
tion. This was centrifuged and the supernatent fluid brought, by further addition of
phosphate buffer solution, to the same volume as the culture fluid. This was then filter-
ed alone or mixed with the culture fluid through an EK Seitz filter. The filtrate was
stored in the refrigerator. Sometimes filtration was not resorted to, but the super-
natent fluid was collected after ultra-centrifugation.
For making the vaccine, 40 parts of the culture fluid was mixed with 60 parts of
aluminium hydroxide. One brew, the fourth, was made in two concentrations, the
one intended for the first vaccination containing 10 per cent culture fluid and the other
intended for the second, containing 20 per cent of the culture fluid. Four brews were
made, the first and second from " Riems O ", the third from " Hansen -Fionie " and
the fourth from " Virus 2 ". Five calves were vaccinated. Four of these contracted
foot-and-mouth disease during the contact test. The fifth one (a " Riems O ") with-
stood contact test, but was susceptible to the " tongue-test ".
(ii) Tissue extract vaccine.—Aphthous membrane was obtained from one or more
infected animals, and crushed with quartz sand. After ultra-centrifugation (at 15,000
for 15 minutes), the extract was diluted in physiological saline solution to increase it
to about ten times the weight of the tissue. Each brew of vaccine was made in two
concentrations—the one intended for the first vaccination containing 20 parts of the
extract and 80 parts of aluminium hydroxide, and the other intended for the second
vaccination containing 40 parts of the extract and 60 parts of aluminium hydroxide.