Etiology, Pathogenicity. 



441 



the spore-bearing bacillus a pin-like or drum-stick-like appear- 

 ance (Fig. 68). In cultures it may form longer sliglitly curved 

 threads. 



Staining. The tetanus bacilli stain readily and uniformly with the 

 usual aqueous anilin dye stains as well as by Gram's method. 



Cultivation. The tetanus bacilli are anaerobic, but 

 develop also in the presence of oxygen when associated 

 with aerobic bacteria which energetically consume 

 oxygen. Under anaerobic conditions they grow readily, 

 especially on media containing grape-sugar, at body 

 temperature, less readily at room temperature. On 

 gelatin and agar the colonies form grayish-white spots 

 composed of clumps of fine threads, while a white 

 streak develops at the point of inoculation, with radia- 

 tions in all directions (pine tree shapes Fig. 69) Gela- 

 tin is liquefied slowly, bouillon is clouded uniformly, 

 milk is not coagulated; on potatoes there is sometimes 

 formed a colorless, transparent deposit. The interior 

 of an extirpated eye is also well adapted for its cultiva- 

 tion (Mackie). Gas (CH^, COo) is produced on sugar- 

 containing media and the cultures disseminate a 

 peculiar burnt odor. Spore formation begins in the 

 bacilli, under favorable conditions, after 24 to 30 hours. 



Tenacity. Since most of them are sporebearing, the bacilli 

 are almost as resistant as the spores. Direct sunlight destroys 

 them in 12 days, diffuse light in 1 to 2 months (Vaillard &A^incent). 

 In decomposing material they remain alive for a long time and 

 may increase for a time according to experiments by Bombieci. 

 Wlien kept in a dark place they are still virulent after 11 years 

 (Henrijean), and in pus and animal tissues they retain their 

 vitality for months (Kitt). Cultures retain their vitality for two 

 years (Kitasato). The spores are killed by live steam at 11.5"C. 

 in 5 minutes, by .5% carbolic acid in 15 minutes, by 1:1000 corro- 

 sive sublimate and 1^% hydrochloric acid solution in half an hour 

 (Kitasato), by a 1% nitrate of silver solution in 1 minute, by 

 5% creolin solution in 5 hours (Tizzoni & Cattani). The addi- 

 tion of iodine trichloride in the proportion of 0.125-0.25% to 

 culture decreases the virulence proportionally to the quantity of 

 the drug (Behring & Kitasato). The digestive juices have a very slight destructive 

 action (Sormani). 



Pathogenicity. Fresh cultures are so slightly virulent that 

 guinea pigs which are very susceptible to tetanus can stand a 

 subcutaneous injection of 0.3 or 0.5 cc. without harm, but 

 cultures ten days old or older ^vill in very minute quantities 

 produce tetanus in susceptible animals. Filtrates of such cul- 

 tures free from bacilli and spores act similarly and only after a 

 certain period of incubation, showing that living cultures exert 

 their pathogenic properties by means of toxic products (in 

 aerobic mixed cultures there develop similarly acting toxins 

 as in pure anaerobic cultures). Spores freed of their toxins by 

 prolonged washing or heating for 3 hours at 80° C. prove in- 

 effective upon subcutaneous injection even when given in rela- 

 tively large quantities, while these same spores wdien injected 

 subciitaneously or brought under the skin in small paper sacs 



Fig. 69. Four' 

 day old agar cul- 

 ture of tetanus 

 bacilli. 



