56 THE MILK SITUATION IN THE DISTRICT OF COLUMBIA. 



that tubercle bacilli of the bovine type are, as a general rule, more 

 virulent than those of the human type for all animals. 



Of prime importance in the eradication of tuberculosis is the pos- 

 session of some adequate means of diagnosing its symptoms during 

 the period of incubation and in its preliminary stages, so as to avoid 

 the communication of the infection from the affected individual long 

 before the existence of the disease may be established by clinical 

 examination. 



DISCOVERY OF TUBERCULIN. 



This diagnosis has been made possible for animals by the epoch- 

 making discovery of tuberculin in 1890 by Dr. Robert Koch, the 

 world-famed specialist on tuberculosis. Tuberculin is the sterilized 

 and filtered glycerin extract of cultures of tubercle bacilli. It does 

 not contain the bacilli themselves, but the cooked products of the 

 growth of these bacilli. When injected under the skin of a normal 

 animal no effect whatever is produced. If, however, the animal is 

 tuberculous a decided rise of temperature ensues. 



Tuberculin was first used experimentally in treating tuberculosis 

 in man. The fact that its injection occasioned a rise in temperature 

 in tuberculous persons led veterinarians to apply tuberculin similarly 

 to animals, and since 1891 the use of tuberculin as a diagnostic agent 

 for tuberculous cattle has been almost universally availed of in all 

 parts of the civilized world. 



METHOD OF APPLICATION OF TUBERCULIN TEST. 



The test is applied in practice by taking the temperature (usually 

 three times at intervals of 2 hours) to ascertain the normal varia- 

 tions of temperature of the animal to be tested. The dose of tubercu- 

 lin is then injected hypodermically between 8 and 10 p. m. on the 

 same day, and on the following day, beginning at 6 a. m. and continu- 

 ing until 20 hours following the injection, temperatures are recorded 

 every 2 hours. If the temperature increases, the animal is said 

 to " react," or in other words to respond to the test, which reaction 

 indicates conclusively in general that tubercular infection exists. 



IMPORTANCE OF TUBERCULIN AS DIAGNOSTIC AGENT. 



This infection may be absolutely unobservable and undetectable 

 visually. There may be nothing whatever to indicate an unhealthy 

 condition in 'the animal, which may be fat, sleek, and apparently in 

 the most robust health, even the most careful detailed clinical exami- 

 nation failing to evidence the diseased condition. It is this well- 

 established fact that a cow may be experiencing a considerably 

 advanced stage of tuberculosis and not give evidence of the existence 

 of the disease in any outward appearance on the closest physical 

 scrutiny that makes the tuberculin test an invaluable asset in estab- 

 lishing the diseased condition in time to prevent the spread of the 

 infection to other animals in the herd, as well as to insure against the 

 intermittent contamination of the milk of the diseased animal by 

 tubercle bacilli. 



It is estimated by the authorities consulted by the committee that 

 from 24 hours to 3 days is requisite for applying the test, the 



