METHODS OF EXAMINING MILK 225 
shipped some distance to a laboratory to be tested for 
specific gravity, fat per cent., and per cent. of total solids, 
or to be subjected to any of the chemical tests, an anti- 
septic may be added to preserve them. Potassium dichro- 
mate, 4% gram to the liter of milk (714 grains to the 
quart) and formalin, 20 drops to the liter, are usually 
used for this purpose. It is better, however, to sterilize 
the sample bottle by boiling and to close it with a steril- 
ized stopper. This method must be followed when bac- 
teriological or ferment tests are to be made, as antiseptics 
cannot be added in such cases, and the samples should 
be packed in ice. 
Stable or Herd Samples.—When a sample of market 
milk is tested and it appears from the results that the 
milk has been diluted with water or that it has been 
skimmed or diluted with skimmed milk, a stable or herd 
sample may be taken at the dairy farm from which the 
suspected milk came and tested for comparison. On the 
day the herd sample is taken, the cows should be fed, 
watered, and milked as usual and by the regular persons; 
the two milkings should be thoroughly mixed and the 
sample taken from the whole. If nitrates or nitrites have 
been found, samples of the water should also be taken 
and examined. The importance of the stable or herd 
test is variously regarded. Some authorities do not con- 
sider it of much value, especially for small herds, because 
of the daily variation in the composition of the milk of 
the cow, particularly in the per cent. of fat. Others do 
not believe that accepted averages of the specific gravity 
and composition of normal milk are a safe basis for judg- 
ing milk in regard to dilution or skimming, and are of 
the opinion that a definite conclusion can only be reached 
15 
