1895-96.] Mr D. F. Harris on Chemistry of Milk. 
73 
it is these that are held to he caseinogen exclusively, while the 
globules are said to be only fat. Optically, however, all these 
particles behave alike ; the smallest refract light exactly as do the 
largest, but when one set are focussed the others are out of focus, 
so that they do not all look bright or dark at once. Further, all 
these particles appear to stain with 1 per cent, osmic acid. 
Neither globules nor granules could be stained with any of the 
following : — Carmine, picrocarmine, hematoxylin, and eosin, and 
I have completely failed to demonstrate the presence of an envelope 
or membrane round the globules, much less to prove the assertion 
that it is of equal thickness round particles of all sizes, as is asserted 
by Oliver.* 
We are warranted in asserting that the union of fat with casein- 
ogen is an exceedingly intimate one, whether the proteid be a 
membrane or be interstitially associated with the fat, and may, I 
think, say that whereas the globules consist of a maximum of 
fat and a minimum of caseinogen, the granules have a minimum of 
fat and a maximum of caseinogen. It is familiar to chemists that 
if we try to precipitate the caseinogen we precipitate the fat, and 
if we try to clot the caseinogen we entangle the fat ; in short, what- 
ever happens to the caseinogen happens to the fat, and vice versd. 
With the microscope I scrutinised a large number of clots, pre- 
cipitates, and wheys to find a striking similarity in all. The acetic 
acid-precipitate in milk consists of masses of the very smallest 
particles agglutinated together, many of the globules being present 
along with them — the so-called “ precipitate of caseinogen en- 
tangling the fat.” There is not an appearance of fibre. But 
cream itself, “ the fat,” par excellence , is, when treated with acid, 
microscopically the same thing, save that the relative proportion of 
globules to granules is reversed. 
A morsel of the clot (produced by rennet) is, under the micro- 
scope, extremely like the acid-precipitate — a multitude of fine 
granules cohering with great tenacity, with relatively few globules 
caught amongst them. There is no vestige of fibrillation. The 
precipitate by saturated sulphate of magnesium is, again, an aggluti- 
* Late Principal of the Western Dairy Institute, Berkeley, in his work 
On Milk , Cheese , and Butter , p. 34. 
