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ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 105 
A very remarkable observation has been made by Kredil and 
Lenk (Biochem. Zeit., 36, 357, (1911)). They assert that sterile milk 
contained in sterile vessels will not clot when treated with sterile 
rennet. If, however, one dips into the mixture a non-sterilised body 
such as the finger or a glass rod, clotting sets in. A few drops of 
ordinary milk will also cause clotting. 
In conclusion attention is directed to a most interesting paper by 
- Bordas and Touplain on “ Reactions of Curdled Milk due to the 
Colloidal State ” (Comptes Rendus, 150, 341 (1910)), where the view 
is advanced that the reactions of curdled milk hitherto attributed to 
the presence of enzymes may be explained by the colloidal state 
of the casein. 
The Cellular Content of Milk. 
Milk contains a large number of cells, falling into three main 
classes :— 
(1) large uninucleated cells ; | 
(2) multinucleated cells ; 
(3) small uninucleated cells. 
These cells are formed either from the epithelium of the gland, or 
from blood and lymph. They may be estimated by centrifuging a 
given quantity of milk, e.g., 10 cc. (preferably warmed to about 
70° C.) and examining the sediment by a microscope. Very varied 
results are given, thus Russell and Hoffmann obtained figures varying 
between 4,000 and 1,000,000 cells per 1 ce. milk. 
Cf. Hewlett, Jowr. of Hyg., 13, 87 (1913); Howlett and Revis, Lancet, p. 855 
* (1915) ; Ross, Jour. of Inf. Diseases, 1Q,7 (1912); Russell and Hoffmann, Jour. of 
Inf. Diseases, 8, Suppt. (3), 63 (1910). 
Detailed knowledge of the nature of the cellular content of milk 
is still meagre, and the subject is only referred to here, as indicating 
another factor in the very complex colloidal nature of milk, since 
modern colloid chemistry is no longer the study of undialysable or 
glue-like substances, but of matter in a finely divided form, thus 
embracing grains, bubbles, capillary structures, animal cells, etc., 
and indeed any system of at least two phases, involving extensive 
surface areas. 
The cell content of milk is mainly of interest to histologists who 
are investigating its relation to disease in the cow. See “ Public 
Health Depi., Washington. Report No. 78 (1912).” ; 
Homogenised Milk. 
Homogenised milk is the term given to milk which has been 
heated to 50-60°C, and then forced under great pressure through very 
small orifices, thus redcing the fat particles to very small diameters, 
@.g.,1/100th of the original size. When such a milk is allowed to 
stand, practically no cream separation occurs at all, the milk remain- 
ing a homogeneous system. 
This change in the dispersity of the fat leads to phenomena well 
_ known in colloid chemistry. The extension of surface area of the 
me 
iA 
fat leads to greatly increased adsorption of the milk serum, and the 
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