386 BACILLI IN CHRONIC INFECTIOUS DISEASES. 



Sawizky has recently (1891) made a series of experiments to de- 

 termine the length of time during which dried tuberculous sputum 

 retains its virulence. He arrives at the conclusion that virulence is 

 not suddenly 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-m.entioned 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 

 diminished 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 

 from 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 



