536 PATHOGENIC ANAEROBIC BACILLI. 



The researches of Tizzoni and Cattani show that tetanus spores 

 preserved upon silk threads become attenuated after a time when 

 preserved in a dark place in free contact with the air. Very viru- 

 lent cultures liquefy gelatin, give off a very disagreeable odor, 

 and have a decidedly alkaline reaction. Less virulent cultures 

 quickly acquire an acid reaction. Cultures of which the virulence 

 is very much attenuated grow more rapidly and abundantly than 

 virulent cultures and produce more gas in hydrogen at 37 C. ; they 

 do not liquefy gelatin and have no odor. In attenuated cultures de- 

 generation forms are often seen, and the spores are frequently elon- 

 gated or almost rod-shaped. Cultures preserved in various gases 

 for thirteen to fourteen months invariably become attenuated. 



Immunity. Kitasato was not able to produce immunity in mice 

 by inoculations with minute doses of the poison, or with a filtrate 

 which had been exposed to various degrees of temperature by which 

 its activity was diminished or destroyed. But immunity lasting for 

 about two months was produced in rabbits by inoculating them 

 with the filtrate from a culture of the tetanus bacillus and subse- 

 quently, in the same locality, with three cubic centimetres of a one- 

 per-cent solution of terchloride of iodine ; this last solution was in- 

 jected subcutaneously in the same dose at intervals of twenty-four 

 hours for five days. Of fifteen rabbits treated in this way six proved 

 to be immune against large doses of a virulent culture of the tetanus 

 bacillus. The same treatment was not successful in producing im- 

 munity in mice or guinea-pigs, but the important discovery was 

 made that a small quantity of blood (0. 2 cubic centimetre) from an 

 immune rabbit, when injected into the abdominal cavity of a mouse, 

 gave it immunity from the effects of inoculations with the tetanus 

 bacillus. Moreover, mice which were first inoculated with a virulent 

 culture of the bacillus, and, after tetanic symptoms had appeared, re- 

 ceived in the cavity of the abdomen an injection of blood serum from 

 an immune mouse, were preserved from death. The power of the 

 blood of an immune animal to neutralize the tetanus poison was fur- 

 ther shown by mixing the filtrate from a virulent culture with blood 

 serum from an immune animal and allowing it to stand for twenty- 

 four hours ; a dose three hundred times greater than would have 

 sufficed to kill a mouse proved to be without effect after such admix- 

 ture with blood serum as before stated, the blood serum of animals 

 which are not immune has no effect upon the poison. The duration 

 of immunity induced in this way was from forty to fifty days. 

 Blood serum from an immune rabbit, preserved in a cool, dark room, 

 retains its power of neutralizing the tetanus poison for about a week, 

 after which time it gradually loses it. Having found that chickens 

 have a natural immunity against tetanus, Kitasato made experiments 



