Counting leukocytes to provide a wholesome milk-supply Part 3

Since in milk “good” streptococci cannot be distinguished from “bad” cocci to characterize the quality of the milk as “good” or “bad” for consumption, maybe it is possible to evaluate the quality of the milk by looking at the leukocytes in the milk.  After all, given the assumption that the consumption of milk with mastitis streptococci and sore throats and gastrintestinal disturbances in man are causally related, the determination of inflammation markers in milk may offer an alternative solution for such an evaluation. This raises two problems. First, it has to be established that increased numbers of leukocytes indeed reflect increased numbers of cocci; second, that a threshold value can be determined on which milk can be judged as safe or harmful. This subject constitutes the last part of Harris’ paper. (1)

Harris starts to discuss the use of the word “pus cell” that was common usage in his time. “All milk contains leukocytes” he quotes W.G.Savage, a British public health expert. “When does a leukocyte become a pus cell, and what distinguishes one from the other?” The presence of leukocytes in milk up to a certain point is physiological, but beyond that point is pathological. The literature shows large variations in leukocyte number, among cows and among quarters of one cow. Some authors report proportional relationships between streptococci and leukocytes, others cannot find them.

Next, Harris discusses the attempts to develop practical methods of leukocyte counting. These methods are mostly based on staining cells in known volumes of milk and counting them with a microscope and a hemocytometer; the staining procedures are complicated and time consuming, but Harris consideres them as good.  An alternative method is the use of the tube developed by Trommsdorff, that is filled with 5 ml of milk, centrifuged, and the volume of the sediment read of as a measure of cell number, bur Harris is not very positive about it.

(from a recent catalogue of Gerber Instruments)

One of the authors he mentions had stated that milk containing 500,000 cells per c.c. togther with the presence of fibrin (an inflammation marker, BN) is to be regarded as suspicious, whereas a cell number of one million per c.c. and associated with fibrin “is conclusive of the presence of pus, i.e., evidence of mastitis.

In the next blog I will discuss Harris’ conclusions.

1. N.M.Harris, ‘The relative importance of streptococci and leukocytes in milk’, The Journal of Infectious Diseases, 4 (1907) 50-62.