MICROSCOPICAL EXAMINATION OF MILK milk appears under the microscope to be composed of free, structureless milk globules, which contain the fat. These circular disks become angular in cooling and present a corrugated surface, be cause the fat, which at an earlier stage was still in process of cooling, has grown rigid. They are now cream globules. The diameter ranges between 0.9 and 22 microns (red corpuscles of human blood 5 to 9 microns). In a microscopical view of undiluted milk, when it is rich in fat, the globules of medium size, from 2 to 5 microns, predominate. The smaller sizes become prominent only in diluted milk or in that which contains but little fat. As many as 11 millions of globules may some times be counted in a cubic millimetre; the average number is about 5 millions. The proportion of the different sizes is nearly uniform. In eow's milk 4 to 10 per cent. are over 4 microns, 25 to 30 per cent. are over 2 microns, 60 to 69 per cent. are under 2 microns.
For such investigations, which have not yet been extended to human milk, the milk must be diluted a hundred-fold and one drop placed under the microscope. The size of the globules is ascertained by the micrometer.
Hooded milk globules having a fringe or surrounded by plasm, are frequently found, along with leucocytes, in the creamy part of human milk, and invariably so in its centrifugalized sediment, but more rarely in the milk of animals which give a copious yield. By the addition of acetic acid, or by coloring with methylene blue, a flattened nucleus is generally brought into view. We have here a trace of the characteristics of the colostrum stage, which does not, however, justify any conclusion as to the quality of the milk. A too abundant appearance of these and other constituents of colostrum, whose presence is shown also by the strength of the reactions with superoxides, peroxides, and reducing agents, indicates abnormal conditions preceding the colostrum period itself. These conditions, however, might originate in some defect of the lacteal glands or be produced later by failure to exercise the glands. Colostrum contains in addition (1) the peculiar colostrum cles, which are large, dark cells filled with fat globules of all sizes. After their removal by ether, a protoplasmic vacuole, haying a large nucleus which is faintly colored by the pigment cells, makes its appearance. (2) Mononuclear or polynuclear lettcocytes, highly colored. Whether
the first named, when they contain drops of fat, are to be reckoned as colostrum corpuscles is, for the present, undetermined; some at least are found which resemble colostrum corpuscles in the slight coloring of the nucleus. (3) Lymphocytes; and (-1) clotted portions, which receive a faint color from the pigment cells and mire turned blue and red by iodine and sulphuric acid respectively.
The microscopical investigation of human colostrum has reeeivNI some practical significance through the assertion of Weill and Thevenet that a predic tion as to the subsequent yield of milk can be based upon it.
To demonstrate centrif agate 1 to 2 c.c. of colos trum, shortly after delivery. After diluting with a physi ological solution of sodium chloride, remove the layer of cream. decant the milk, draw up the sediment by means of a pipette, and spread it evenly on a microscope slide. This smear is placed for 24 hours in a mixture of equal parts of alcohol and ether, stained for 15 minutes in alum htem a toxylin and for 7 minutes in a rose-colored watery so lution of eosin. If there are more than 70 per cent. of polynuclear leucocytes the prognosis is favorable, and if more than :50 per cent. of lymphocytes it is un favorable. In a majority of cases, however, the figures admit of no positive prediction.
The constituents of colostrum disappear in women as soon as the secretion of the milk and the suckling of the infant are well in progress, which is usually by the end of the first week. It is important to differen tiate these constituents from those of inflammation of the mammary gland and duct. In this disease numerous polynuclear leucocytes and micro-organisms are present in the milk. (Testing the first drops is useless.) Fever may at first be absent.
Microscopical investigation of human milk—leaving out of the question the knowledge to be acquired of the properties of colostrum— has a practical value only in so far as a sufficient abundance of fat proves the quality of the milk. Poverty in fat, which is evidenced by the appearance of very small fat globules, cannot be inferred from microscopic examination of the first flow of milk.
In counting the fat globules, it is best to employ the stage usually used for counting blood corpuscles, taking the necessary precautions.
The microscopic examination of cow's milk sometimes reveals the presence of bacteria.