On conditions necessary to obtain a clean milk supply and on methods of testing cows' milk in relation to standards of cleanness : report to the Sub-committee on clean milk / by S. Delépine, June 16th, 1918.

  • Delépine, Sheridan, 1855-1921.
Date:
1918
Catalogue details

Licence: In copyright

Credit: On conditions necessary to obtain a clean milk supply and on methods of testing cows' milk in relation to standards of cleanness : report to the Sub-committee on clean milk / by S. Delépine, June 16th, 1918. Source: Wellcome Collection.

    10/116 (page 8)
    mined by the size of the centrifugal machine available. (Before 1906 I had to use a centrifugal machine made in Germany. Since then I have used a better and larger one made in Manchester, in which 16 large samples can be centrifugalised at the same time and at a high constant speed.) The volume of sedunent is estimated in parts of moist sediment per 100,000 parts of milk, so that a difference of 10 cc. does not affect the value of my record, the oldest of which are quite comparable with the most recent. Centrifugalisation is used not only for the purpose of estimating the amount and general characters of the extraneous and cellular products {slime of dairymen), but also to separate these products for purposes of microscopical examination and inoculation. Until about 12 years ago the sediment was generally obtained and measured at one operation, but, even then, v/hen very accurate mea^sure- ments were required the operation was conducted in three steps and the sediment was washed before being measured. Of late years the last method has been used in preference to the simpler one, but this has affected the results only in minor details. The general adoption of the more elaborate method has been made possible by various improvements in the apparatus used. Simple method.—(Unwashed sediment). 50 cc. (If ounces) of well-shaken milk is poured into a strong glass tube of standard diameter, the bottom of which is hemispherical. The tube is placed in a centrifugal machine (effective diameter 17) run for 15 minutes at a speed of 2,000 increasing gradually to 3,000 revolutions per minute for 15 minutes, (f.e., the bottom of the sedimentation tubes travel at the rate of a little over 21 miles per minute). After this operation, unless the milk is distinctly abnormal, the cream forms on the surface of the fluid a layer so firm that the tube can be turned upside down without any spilling of milk. The greater part of the cellular and extraneous products, including bacteria, form at the bottom of the tube a sediment (slime) so dense and compact that, after removal of the cream, the separated milk contained in the tube can be poured out without the sediment being displaced. The bulk of the slime can be estimated with a fair amount of accuracy by measuring the diameter of the sediment. Tables giving the relation between the diameter and bulk are used for that purpose. The colour and other characters of the various parts of the sediment can also be observed. Elaborate method.—(Washed sediment). The sediment may either be obtained in the kind of tubes described above or in metal tubes, the lower part of which forms a chamber contain¬ ing a small glass tube in which the sediment is collected. By opening this chamber the small glass tube can be removed.