XXVni PEESIDENTIAL ADDEKSS. 



It may be asked, What is tuberculin, and how is it applied ? 

 Tuberculin is a simple glycerine extract of the toxic products of a 

 broth culture of the tubercle bacillus ; but its preparation, 

 although not at all difficult, requires very special care. 



A culture of tubercle bacilli in .i^lycerine nutrient medium of 

 special formula, after five or six weelcs in the incubator at a 

 uniform temperature of 87 deo-rees centigrade, is sterilized in an 

 autoclave at 110 degrees centigrade ; it is then concentrated in 

 vacuo in the presence of sulphuric acid till the bulk of the culture 

 is reduced to a tenth part of the original quantity, then passed 

 through a specially designed Pasteur-Chamberland porcelain 

 filter under an air pressure of about 400 pounds on the square 

 inch, which strains all the remains of the dead bacilli from the 

 liquid, and afterwards kept in well stoppered bottles and protected 

 from light and heat. As the original culture contained 5 per 

 cent, of glycerine, the evaporated product contains about 50 per 

 cent., which explains why it retains its activity for so long. 

 During the inoculation of a large number of flasks of nutrient 

 media on different occasions, the number of tubercle bacilli in- 

 troduced cannot possibly be the same in quantity for every flask ; 

 it therefore naturally follows that there must be a corresponding 

 difference in the quantity and quality of the tuberculin produced. 

 This difficulty can only be overcome by the delicate operation 

 of " standardising," which is carried out by injection of the 

 tuberculin into healthy guinea-pigs. 



On the Use of Tuberculin. — The injection of tuberculin in 

 recognized standard quantities is always inocuous ; performed 

 on milking cows, it in no way affects either the quantity or quality 

 of the milk produced, and it in no Avay interferes with gestation, 

 even in animals about to calve. The usual practice in applying 

 tuberculin as a means of diagnosing tubercolosis in cattle is first 

 of all to determine the normal temperature of the animal, which 

 is done by the use of the clinical thermometer. For ordinary 

 purposes tuberculin is employed diluted to the extent of one-tenth 

 in carbolized water, 5 per 1000. The best plan is to inject at 

 one time beneath the skin behind the shoulder 3 to 4 cubic 

 centimetres of the dilution (8 cubic centimetres for cows of 

 medium size, 3^ for large cows, and 4 for bulls and high-class 



