View report page

65
presenting no evidence whatever of disease in the mammary gland. Polynuclear
leucocytes are the cells especially characteristic of acute inflammation, and are the essential
ingredients of pus. But in view of the above facts it is clear that no milk should be
accused of containing pus unless such cells are present in immoderate and
disproportionate numbers.
The bacterial content of fresh milk is of various nature. It is unavoidable'that it
should contain certain microbes from the skin of the cow and the milker, and amongst
these are staphylococci, sometimes staphylococcus pyogenes aureus. The chief source of
bacterial milk pollution is cow dung, so abundantly present on the hind quarters and
belly of the animal and even on the udder. Unless the most exceptional care is taken,
some admixture of cow dung with milk is the rule. The main organisms in milk are
thus of excremental origin, and include streptococci, bacillus coli, and bacillus enteritides
sporogenes. In fresh milk, as sold in shops, these organisms are invariably found in
numbers proportional to the original pollution of the milk and to the temperature at
which it has been kept during the interval since milking. Thus it is common to find
1,000 or more B. coli and 1,000 or even 10,000 streptococci per c.c. of milk, for these
organisms multiply rapidly unless the milk is kept very cool. But staphylococci are not
usually found in such large numbers.
The Cellular and Bacterial Content of Preserved Milk.
Here, as I have already said, our knowledge is much more scanty. As regards the
cellular content I have had to make my own observations. I have taken as a standard
the best whole milk imported uncondensed in tins and sterile on culture. These have
furnished the following results :—
Sample 1—Total cells 2,200 per c. mm.—60 per cent, polynuclears.
„ 2 „ 830 „ 62 „
„ o „ 3o0 „ 57 „ y
,, 4 ,, 660 ,, 57 ,, ,,
n ^ n a 66 ,, ,,
„ 6 „ 480 „ 67 „ „
a 7 a 2,100 „ 73*5 „ ,,
(The last sample was not quite sterile on culture.)
It will be apparent from these figures that the high-class preserved milks have a
cellular content much the same as normal fresh milk, as might have been anticipated.
But if they are diluted and allowed to stand in a conical glass, a sediment is obtained,
which in a stained film presents a colourable imitation of pus, so far as its cytological
aspect goes, though it differs in the absence of pyogenic microbes. In examining
stained films of the sediments from the seven high-class unsweetened milks just menrioned,
I found one group of ill staining and probably dead staphylococci in each of two
samples ; otherwise not a single microbe was seen.
The Cellular Content of Condensed Machine Skimmed Milk.
Stained films from the sediments from these may show no greater apparent
abundance of cells than a high class milk. In other cases, and these the more frequent,
the cells appear more frequent in films, sometimes very much more numerous.
Nevertheless, actual counts of the number of cells per c. mm. are no higher than in
good milk. (The highest count I have obtained is 1,800 per c. mm. of the undiluted