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IOWA ACADEMY OF SCIENCE 
in turn are disintegrated. It is believed, however, that some cells, possibly 
the largest number, simply discharge their fat droplets and other con- 
tents into the lumina, while otherwise remaining intact. To support the 
first mentioned idea, Steinhaus and Szabo report actual evidence of 
mitotic cell division in the actively secreting glands, the daughter nuclei 
taking part in the general disintegration. 
The precise method of the formation of fat in milk is not known. It 
occurs in the milk in the form of innumerable globules, covered with a 
thin layer of casein. These vary in diameter from .001 to .005 mm. 
and give color to the emulsion by the reflection of light. The relative 
numbers of larger and smaller globules in milk is somewhat affected by 
the breed to which the producing animal belongs. It is commonly recog- 
nized that there is a higher percentage of large globules in Jersey and 
Guernsey milk than in Ayrshire and Holstein milk, since the emulsive 
power of the former is less than that of the latter, permitting the cream 
to rise more rapidly. This fact might suggest a factor in inheritance 
similar to the intensity factors found in color inheritance. 
In a microscopical examination of a large number of samples of milk 
of various composition, it was found convenient for comparison to 
divide the globules into three classes, as regards size. All under .0016 
mm. in diameter were in the first class, those ranging from .0016 to 
.0032 mm. in diameter fell into the second group, and all over .0032 mm. 
were placed in the third class. 
Numerous counts of the globules were made in samples of milk of the 
following fat content: 2.8%, 3.2%, 4.2%, 5.2%, 6.2%, and 7.2%. There 
was found to be a positive correlation between the percentage fat com- 
position of the milk and the number of fat globules of different sizes, 
the co-efficient being .19. From an inspection of the counts, the relation 
is evident, — for instance in the sample of 2.8% fat content, 66% of the 
number of globules were in the first division, 28% in the second and 
6% in the third division. In the 7.2% milk there were only 47% of 
the total number of fat globules in the first division, while there were 
40% in the second and 16% in the third, — showing at a glance the large 
increase in the proportion of large globules, with the increased fat 
composition of the milk. 
The grouping of the globules according to the system mentioned, was 
purely arbitrary. Under a different grouping the correlation might be 
even more evident. But the results were positive enough to warrant the 
conclusions drawn. Continued investigation along this line should reveal 
some facts of great value to the practical producer. 
