584 
On a New Method of Testing Milk. 
up comparativelj little cream, may nevertheless be rich in 
butter-fat. 
The second disturbing circumstance in the use of this instru- 
ment lies in the fact that milk which has suffered agitation by 
travelling long distances by railway, or which has been much 
shaken in passing from the hands of the wholesale dealer to 
the retail dealer and distributer of milk, throws up less cream 
than that which has not been much disturbed. In fact, the 
more or less violent agitation of milk has the effect of breaking 
up some of the cream-globules, in consequence of which the 
cream thrown up by such milk, although apparently thin, 
nevertheless is richer in fatty matter than the cream of milk 
which has not been subject to agitation or suffered a partial 
churning process. 
More reliable indications of the richness of milk in butter-fat 
than the ordinary creamometer, which shows the percentage of 
cream by measure, are obtained by instruments constructed on 
the optical methods of examination. 
Donne's Lactoscope is an instrument constructed on the optical 
principle of testing milk, but, for some reason or other, it has 
not been received with general approbation. 
A far more simple lactoscope, based on the same principle as 
Donne's, has recently been invented by Professor Feser, of 
Munich, under whose directions it is now made by Mr. Johannes 
Greiner, philosophical instrument maker, Munich. Every in- 
strument sent out from Mr. Greiner's workshop is verified and 
certified by Professor Feser to have been properly graduated. 
In England, Feser's lactoscope can be obtained at a moderate 
cost from Messrs. Aug. Bell and Co., of 34, Maiden Lane, 
Southampton Street, W.C., who also supply a complete set of 
apparatus for testing milk, including besides Feser's lactoscope, 
a delicate thermometer, and a lacto-densometer for taking the 
specific gravity of milk, which latter instrument also affords 
very useful indications of the quality of milk. 
Milk rich in cream, as is well known, is more opaque than 
that from which more or less cream has been removed by 
skimming, or to which water has been added. Professor 
Feser's lactoscope is based on the principle of measuring the 
comparative opacity of milk, and thereby determining its rich- 
ness in cream-globules or fat. 
The following woodcut represents Feser's lactoscope — half its 
natural size. It consists, it will be seen, simply of a graduated 
wide glass tube, closed at the attenuated end, and having at the 
other end an aperture which can be closed by placing the thumb 
upon it. In the attenuated part of the tube a smaller cylindrical 
closed tube is fused in, made of white or (so-called) milk-glass ; 
