86 Milk and Its Products 
and the surrounding circle painted in segments of 
varying shades to represent cream, very rich milk, 
normal milk, poor milk, ete. A drop of the milk 
to be tested is placed in the central depression 
and covered with a glass plate, so that a layer of 
uniform thickness is always obtained. The opacity 
of this drop of milk upon the black background 
of rubber is then compared with a corresponding 
segment of the circle. In so far as the fat 
measures the opacity of the milk, this is a fairly 
reliable test; and, used in connection with a specific 
gravity lactometer, a person with some experience 
can readily detect suspected samples of milk, although, 
of course, it is not possible to estimate very closely 
the amount of adulteration or the quality of the 
milk. The pioscope has been used very generally 
and successfully by milk inspectors and those hav- 
ing the control of city milk supply. 
Feser’s lactoscope is another instrument designed 
to determine the quality of milk by opacity. It 
consists of a glass cylinder, in the center of which 
is fixed a white rod graduated with black lines. 
A certain amount of milk is put into the cylinder, 
and by its opacity renders the black lines upon 
the central standard invisible. Water is then added 
to the milk in measured quantity until the black 
lines can be seen, the amount of water so added 
indicating the quality of the milk. This instru- 
ment is more delicate than the pioscope, but it can 
not be so quickly and readily used. The results 
it gives are of very much the same nature and 
