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, % gram to the liter of milk (7% 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 



