December, 1953] C. S. DHARMARAJAN, R. V. RAO AND N. N. DASTUR 263
A study of Fig. 1, wherein the changes in the freezing point have been recorded
for complete lactations, showed that the variation in the case of cows may be roughly
divided into four stages. During the first 12 days of lactation the values were high,
from 12 to 120 days the values were a little below the average for the rest of the
lactation, from 120 to 220 days values fluctuated about the average, and the end
period when the values were a little higher. However, in the case of the two buffaloes,
apart from the colostral period, the other three stages were not so well defined.
Aschaffenburg and Veinoglou [1942-44] in a study with Shorthorn cows found no.
relationship between the freezing point and the stage of lactation, the age of the
cow, or the milk vield.
Effect of season on the freezing point of milk
The results of examinations of samples from different breeds of cows and
Murrah buffaloes over a period of 13 months have been illustrated in Fig. 2. These
results do not reveal any significant variation which could be ascribed to season.
This may be due to the equitable climate of Bangalore and more or less uniform
rations given to the animals throughout the year. A study of the literature of
other countries, however, does not reveal any uniformity of results as far as the
effect of season is concerned. Thus, Elsdon and Walker [1942] from a study of
their results concluded that abnormal weather had no effect on the freezing point
depression. Earlier, Buchanan and Lowman [1929] found that during the spring
months the freezing point was lower than during other seasons. In recent studies
Aschefferburg and Temple [1941], and Aschaffenburg and Veinoglou [1942-44]
obtained varying results in studies extending over two years and concluded that the
smaller freezing point depression observed during the spring was 'due not to the
season as such but a factor connected with it'. The factor presumably was the
sudden change over to more palatable feeding stuffs from that given indoors during
the winter months. Rees [1949] in studies with bulk market milk in Australia found
the freezing point to show a close seasonal trend reaching two peaks during the
year, in late spring and autumn. The values were further closely correlated with
the S. N. F. content of milk, a conclusion not substantiated by the earlier results
of Stubbs and Elsdon [1934].
Effect of souring on the freezing point of milk
A study of the results in Tables I and II show that an increase in freezing point
depression of milk occurred on souring. A perceptible increase was noted at the
end of 4 to 5 hours in the case of cow milk, and 5 to 6 hours in the case of buffalo
milk. In cow milk the increase in acidity when the samples gave positive boiling
test varied from 0.02 to 0.12 per cent lactic acid, and the corresponding increase
in the freezing point depression varied between 0.006º to 0.046ºC., the average
increase in freezing point depression per 0.01 per cent increase in acidity being
0.0036ºC. (Table III). In case of buffalo milk the increase in acidity when the milk
showed positive boiling test varied from 0.03 to 0.16 per cent lactic acid, and the
increase in freezing point depression at the same stage varied from 0.012º to 0.046ºC.,
the average increase in freezing point depression per 0.01 per cent increase in acidity