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ABSTRACT
[ Vol. XXII, Part IV
Comparative tests on eggs and fowls to determine the point of inactivation
of the virus in the vaccine, during incubation showed that the egg test was less
reliable, the failure of the egg test was probably the result of interference in the
allantoic sac between inactivated virus and the propagation of the residual active
virus. The greater accuracy of the fowl test depended, no doubt, to some extent
on the larger inoculum used.—[R.N.S.].
A Dilution Method for the Milk Ring Test in Bovine Brucellosis Detection. HOLM
G. C., EVELETH, D. F., AND RHEALT, P. L. (1950). Vet. Med. XLV, 400-404
T HE authors have described a dilution method for the milk ring test in bovine
brucellosis. A total of 1,044 milk samples composite of each animal, in 35
herds, were tested undiluted together with sufficient dilutions to reach a negative
end point. A constant amount of antigen, a decreasing amount of milk and an
increasing amount of diluent comprising of a negative milk selected for its lack of
reaction and high butterfat content, were used. The negative diluent was preserved
with formalin and stored under refrigeration without affecting the test. Dilutions
of 1 : 1, 1 : 5, 1 : 10, 1 : 50, 1 : 100, 1 : 200, 1 : 300, 1 : 400 and 1 : 800 in 1 ml.
volumes were employed. Just after making the dilutions one drop of standard
milk ring antigen (supplied by the Bureau of Animal Industry, method of prepara-
tion of the antigen not mentioned) was added to each tube and thoroughly mixed.
The tubes were then centrifuged at 1,500 r.p.m. for 10 minutes. Readings were
made according to the standard of Bruhn and of Roepke. The standard adopted
by the former author after incubating the tubes at 37°C. for one hour is as follows :—
Negative : The creamlayer, white ; milk below, bluish violet.
Doubtful : Whole column, uniformly bluish violet.
Weekly positive : Bluish violet coloured cream layer forming a ring, the milk
column not visibly decolourised.
Positive : Bluish violet ring, milk column perceptibly decolourised.
Strongly positive : Distinct bluish violet ring, milk column totally de-
colourised.
The results of the tests carried out on 998 cows, on the basis of blood serum and
milk ring reactions, and history, vaccination, previous positive reaction and stage of
lactation are tabulated. Out of the 998 cows tested 777, with negative blood
reactions did not react in a dilution higher than the 1 : 10 with milk ring test except
in one case and only 4 in the group of 111 cow tests with suspicious blood titres
reacted higher than the 1 : 10 dilution. A total of 110 cow tests appear in the
group of reactors. Of these, animals which had not been vaccinated gave milk
ring reactions in dilutions of 1 : 50 or higher. The majority of the calf vaccinates
gave milk ring test reactions similar to those observed in the negative and suspect
calf vaccinate groups. One-third of the adult vaccinate reactors and those with
known long standing infection reacted in dilutions below 1 : 50, thereby indicating
that they were becoming ' Cease reactors '.
The agglutination inhibition factor, mastitis, colostrum and secretions from dry
cows, which may interfere in the ordinary ring test, do not appear to affect the
interpretations of milk ring dilution test.—[M.M.S.].