522 Lactose in Milk 
with the cumbersome ‘‘corrections” for the volume occupied by 
the protein-fat precipitates. 
Because of the extreme variations in the sugar content of urine 
it seemed desirable to be able to titrate it without preliminary 
dilution. In the case of milk the circumstances are entirely dif- 
ferent, for the variations in the sugar content of this secretion are 
relatively very small, and a swztable preliminary dilution, without 
any uncertainty and without any approximate preliminary sugar 
titration, can be made. It has therefore seemed to us rather 
better to dilute milk before titrating, though the titration can be 
made quite well without any such dilution. We recommend a 
dilution of 1: 4 (25 ce. in a 100 ce. flask) for cow’s milk and 1: 5 
(5 ec. in a 25 ce. flask) for mother’s milk. In emergencies, as 
when the quantity of human milk available for the sugar titra- 
tion is very small, a dilution of 1:6 (2 cc. added to 10 ce. of 
water) can be used. 
The titration is made as follows: Into a large test-tube intro- 
duce 2.8 to 3.4 ce. of the diluted milk (that is, nearly the full 
amount expected), 5 cc. of a 6 per cent copper sulfate solution, a 
pebble (to prevent bumping), and 4 to 5 gm. of a dry salt mixture 
(made by mixing, in powdered form, 100 gm. of disodium phos- 
phate, 60 gm. of anhydrous sodium carbonate, and 30 gm. of so- 
dium or potassium sulfocyanate). Shake, and boil gently for 4 
minutes before adding any more milk. At the end of this time 
add more milk (0.02 ce. to 0.10 ec., depending on the amount of 
blue color remaining) and boil again. After each addition of 
milk (except the first) boil 1 minute. The total boiling period 
should be 5 to 7 minutes. 
For the measurement of the milk we recommend the 5 ce. 
burette and other accessories, mentioned in the preceding paper 
in connection with the titration of sugar urines.! 
Calculation: 4.04 multiplied by the degree of dilution (4, 5, or 
6) and divided by the titration figure, gives the per cent of 
lactose present. 
1 We have up to date made over 200 sugar determinations by this new 
titration method—most of them on human milk. This work has developed 
into a relatively. extensive study of the sugar content of human milk and 
will be published later. 
