450 MILK 



after infection. This period may cover several years. After the 

 disease has started to develop certain symptoms begin to be 

 apparent. Food does not seem to be well digested, the coat 

 becomes rough, arid the skin loses its normal elasticity. These 

 symptoms are followed by a progressive loss of flesh and, later, 

 by loss of appetite, bloating, and diarrhea. If the lungs are 

 affected a cough develops, and when the disease reaches the udder, 

 hard lumps are felt after milking. When postmortem examina- 

 tions are made, tubercles may be found in any organ. The 

 tubercles are sometimes as small as millet seeds or peas, or may be 

 several inches thick. Inside of the tubercles is a cheesy mass of 

 yellow color or a dry gritty substance. Tubercles of the size of 

 millet seeds or peas are frequently found attached to the peri- 

 toneum. This form of the disease is called "pearl disease" 

 (perlsucht). 



The chief limitation of physical examinations is the failure to 

 disclose the disease at an early stage. Cows may have the ap- 

 pearance of perfect health, may give milk of normal composition; 

 furnish an abundant supply of milk; even feed normally, and 

 still harbor tuberculous lesions which, in the course of time, will 

 develop into advanced tuberculosis. During early stages the 

 animal is an unrecognized source of infectious material, endanger- 

 ing healthy members of the herd and causing contamination of 

 the milk. 



The tuberculin test is sufficiently delicate to disclose the pres- 

 ence of tuberculosis. Tuberculin was first prepared by Koch in 

 1890. For production on a large scale the procedure is as follows: 

 A strain of tubercle bacilli is cultivated from sputum or from a 

 tubercle of an animal dead from the disease. The medium for 

 isolation may be agar, potato, blood-serum, or egg medium with 

 5 to 7 per cent, glycerin added to the medium. After several 

 weeks a surface layer of bacilli will form and a film may cover the 

 surface of the condensation water. From the surface growth or 

 from the film a small amount is floated on the surface of a medium 

 in a large Erlenmeyer flask. This medium is prepared as follows: 

 One pound of chopped beef or veal is covered with 1 liter of water 

 and digested over night. The meat is then pressed out, the vol- 

 ume brought up to 1 liter, and 1 per cent, pepton and 0.25 per 

 cent, sodium chlorid dissolved. The solution is boiled and fil- 

 tered, the reaction adjusted to 0.75 to 1 per cent, acid to phenol- 

 phthalein, and finally filtered again and sterilized. It need not 

 be perfectly clear. It is then filled into Erlenmeyer flasks, each 

 flask to contain 100 to 250 c.c. Tubercle bacilli contain a rela- 

 tively large amount of phosphorus, and Dorset recommends, 

 therefore, to add J per cent, of acid potassium phosphate. 



