March, 1949]
ABSTRACTS
89
0.1 c.c. of milk, previously shaken, on the medium surface by means of a sterile,
bent glass rod. The inoculated plates of PRMS and SM 110 were incubated at 37ºC
for 36 and 48 hours respectively, and colonies were picked up on the basis of fer-
mentation in the former and pigmentation in the latter. To determine the coagulase
activity various methods using fresh, citrated, pooled rabbit blood and plasma were
employed. Slide-clumping test was done according to the technique of Cadness-
Graves et al, and for tube coagulase tests the techniques described by Chapman
and Chapman et al, were adopted. Observations have also been made regarding
haemolytic activity on rabbit blood-agar plates. It has been shown by facts and
figures that SM 110 is more efficient than PRMS, although none of the two is perfect.
Of all the coagulase tests the slide-clumping test was found to be simple, reliable and
quick. Lyophilized blood and plasma proved to be almost as good as fresh blood
and plasma on repeating some of the observations with the former. It is further
shown that coagulase production does not show complete correlation with either
haemolysis or pigment formation on SM 110. All the non-pigmented strains, how-
ever, proved to be negative for haemolysis and coagulase production. The procedure
recommended for the maximum recovery of coagulase producing Stphylcocci from
milk includes the use of both the media with a final confirmation by slide-clumping
test. (G.S.)
THE OPTIMUM STRUCTURE OF BREEDING FLOCKS. I. RATE
OF GENETIC IMPROVEMENT UNDER DIFFERENT BREEDING
PLANS
Dempster, E.R. and Lerner, I.M., (1947). Genetics. 32, 555-66
T HE authors have studied the rates of gain in the production index of birds
of various age distribution under three different breeding plans. They have
stressed that the efficiency of the breeder's operations depends on three factors:
(a) the intensity of selection, (b) the accuracy of selection, and (c) the average interval
between generations. In the plan designated as III, the first selection is made on
two-year old hens, on the basis of the full records of themselves and their sisters.
A year later, the second selection from the group thus chosen is made on the basis of
their part progeny records. Finally, a third selection is made on the basis of the
full records of the progeny at four years of age. In plans I and II, the above pro-
cedure is advanced by a year. Under both these plans, the first selection is made
on the basis of individual and family records of birds which have been in production
for about four months. In plan I, the pullets rejected are not further considered.
The second and third selections are similar to that under plan III except that they
occur one year earlier. In plan II, the pullets rejected on the basis of their part
records are considered at two years of age when they and their sisters hay completed
records.
As regards males, the first selection is made at one year of age, on the basis of
the part records of sisters. At two years of age, the second selection from these
males is based on the full records of the sisters as well as the part progeny records.
The authors have shown that greater efficiency is obtained under plans I and II
than the schemes under plan III. The use of breeding plans involving a high per-
centage of pullets, not only leads to more rapid improvement but also result in a
T