249 



about twenty minutes. If now the supernating fluid be taken 

 off the minute quantity of debris at the base of the tube can 

 be examined right away; or, if the material is required in a 

 purer condition, completely free from caustic potash, a series 

 of dilutions and centrifugalizations with distilled water can 

 be carried on." 



With a drop of the sediment from the bottom of a tube 

 make a smear on a clean cover glass ; stain with Gray's or 

 Ziel's carbol-fuchsin, warm and allow stain to remain five to 

 ten minutes; decolorize for a few seconds in a 10 to 20 per 

 cent, acid solution (hydrochloric, nitric or sulphuric acid); 

 wash in distilled water, dry and mount in balsam. Examine 

 with a one-twelfth or a one-sixteenth-inch oil-immersion 

 objective. The tubercle bacilli will have a distinct red color, 

 while all other germs will be decolorized. 



A few drops of the sediment from the bottom of a centrifu- 

 gdlized milk may be injected into the abdomen, under the 

 skin or into a vein, of a rabbit or guinea pig. In from ten to 

 twenty days the guinea pig will have developed sufficient 

 tuberculous changes to permit one to make an accurate 

 microscopic test for tubercle bacilli. 



The question as to whether a tuberculous cow without 

 apparent tuberculosis of the udder will throw off tubercle 

 bacilli in the milk is not fully determined; but it is very 

 probable that such cows will not give infectious milk. Some 

 authorities have conveyed tuberculosis to pigs by feeding 

 them milk from tuberculous cows : the udder may have been 

 involved in all of these cases. No doubt many infants, chil- 

 dren and some grown persons contract tuberculosis by drink- 

 ing infected milk. If the dairy cows have not been tested 

 with tuberculin for tuberculosis it is always the safest to 

 pasteurize or sterilize the cream, butter and milk that come& 

 from such a dairy. Some have thought that the separator 

 would remove all the germs from the milk and cream, but the 

 fact is that germs remain in the cream and the milk after the 

 process of separation. Consequently dairy herds that supply 

 milk, cream or butter to the public should be tested with 

 tuberculin, and all animals that react should be removed from 



