404 BACILLI IN CHRONIC INFECTIOUS DISEASES. 



Sawizky in 1891 made a series of experiments to determine 

 the length of time during which d ried tuberculous sputum retains 

 its virulence. He arrived at the conclusion that virulence is not sud- 

 denly but gradually lost, and that in an ordinary dwelling room 

 dried sputum retains its specific infectious power for two and one- 

 half months. 



Metschnikoff states that when kept at a temperature of 42 C. for 

 some time the tubercle bacillus undergoes a notable diminution in 

 its pathogenic power, and that when kept at a temperature of 43 to 

 44 it after a time only induces a local abscess when injected subcu- 

 taneously into guinea-pigs. The experiments of Lote also indicate 

 that an " attenuation of virulence " has occurred in the cultures pre- 

 served in Koch's laboratory, originating in 1882 from the lungs of a 

 tuberculous ape. The author named made experiments with cul- 

 tures from this source (ninetieth to ninety-fifth successive culture), 

 and at the same time with a culture obtained from Roux, of 

 Pasteur's laboratory. Rabbits inoculated with cultures from the 

 last-mentioned source developed a hectic fever at the end of two 

 weeks, and died tuberculous at the end of twenty-one to thirty-nine 

 days. Twelve rabbits were inoculated with the cultures from 

 Koch's laboratory ; the injections were made either subcutaneously, 

 into a vein, into the pleural cavity, or into the cavity of the abdo- 

 men. No elevation of temperature occurred in any of the animals, 

 and they were found at the end of a month to have increased in 

 weight. At the end of six weeks one of them was killed and tuber- 

 cular nodules were found in various organs. The remaining animals 

 were killed at the end of one hundred and forty-four to one hundred 

 and forty-eight days. The two inoculated subcutaneously presented 

 no sign of general tuberculosis, but a small yellow nodule contain- 

 ing bacilli was found at the point of inoculation. Those inoculated 

 by injection into a vein showed one or two nodules in the lungs con- 

 taining a few bacilli. In Koch's original experiments rabbits were 

 killed by intravenous inoculation of his cultures in from thirteen to 

 thirty-one days. That this attenuation of virulence depends upon a 

 <liminished production of a toxic product to which the bacillus owes 

 its pathogenic power appears to be very certain, in view of the fact 

 that the late cultures in a series have a more vigorous and abundant 

 development than the more pathogenic cultures obtained directly 

 f r< in the animal body. 



The discovery by Koch of a toxine in cultures of this bacillus, 

 which is soluble in glycerin, and which in very minute doses pro- 

 duces febrile reaction and other decided symptoms when injected sub- 

 cutaneously into tuberculous animals, must rank as one of the first 



