VERMONT AGRICULTURAL REPORT. 137 



fectly harmless, was originally obtained from a specimen of 

 tuberculous sputum. The guinea pigs inoculated with this 

 sputum died in due time from tuberculosis, and the cultures 

 made from the diseased organs served as a starting point for a 

 large and prolific family. By accustoming this germ gradually 

 to liquid food which had a slight acid reaction, we eventually 

 succeeded in elminating its ability to produce tuberculosis 

 when it was inoculated into animals. The germs, however, 

 did not lose the property of producing or secreting their active 

 poisons — those poisons which form the active principle of 

 tuberculin. Cultures of this sort, which have been caused to 

 lose their virulence or pathogenic properties, are called attenu- 

 ated, and we have used these attenuated cultures 10 great 

 advantage since 1893, both in preparing tuberculin and in 

 treating animals, or injecting animals for the purpose of pro- 

 tecting them against an inoculation with virulent tuberculosis 

 or producing in them a serum which may have curative proper- 

 ties. Virulent cultures are also used in preparing the tubercu- 

 lin, and there are always a number of different generations of 

 varying virulence of tubercle bacilli on hand in the laboratory. 



STERILIZING THE CULTURES. 



When the tubercle cultures have grown sufficiently, which 

 requires from one month to three months, depending upon the 

 readiness with which the growth begins (and this is always 

 influenced by the reaction of the media and the condition of 

 the culture from which the inoculations are made), the flasks 

 with their contents are removed from the incubator and placed 

 immediately in the sterilizing oven, which is kept at a temper- 

 ature of about 125 C. The cultures are left in this oven until 

 they begin to boil. In this way the germs are killed, and the 

 plugs in the mouth of the flasks may be removed and the 

 material filtered without any danger of infecting the workers. 

 Of course, in handling tubercle cultures in such large quantities 

 there is always some danger of infection for the people who 

 are doing the work. When proper care is used this danger is 

 of practically no importance ; but as accidents may occur 

 (flasks be broken and their contents spilled upon tables or floor 

 or in other places) , it is a matter of impossibility to avoid all 

 danger. But the discovery that the attenuated germs can be 

 used to advantage for the preparation of tuberculin materially 

 reduces the possibility of clanger to the workers in handling 

 this material. After heating the flasks in the sterilizer the cot- 

 ton plugs are removed and the contents of the flask heated over 

 a flame to boiling and immediately filtered. The germs, which 

 are packed close together, remain upon the filter paper and are 



