SPORING BACILLI 313 



one inch or so below the surface, in fine straight threads, 

 radiating from the needle track. Slow liquefaction, with 

 slight gas formation, takes place. 



In agar stab (glucose agar) : the growth is somewhat 

 similar: 



In glucose broth : slight clouding, with later a thin 

 powdery deposit on the walls of the tube. Ordinary broth 

 is preferred for toxin production. 



On blood serum : growth with liquefaction takes place. 



In milk : acid is formed but no clot. 



On potato : growth is delicate. 



On agar plates : colonies show a compact centre, with 

 loose feathery outline not unlike B. subtilis or anthrax. 



Spores Resist dry heat at 8o C. for I hour ; live steam 

 for 5 minutes ; 5 per cent acid carbolic for 12 to 15 hours ; 

 1 per cent corrosive sublimate for 2 to 3 hours. Direct 

 sunlight diminishes their virulence and ultimately destroys 

 them, otherwise they may remain virulent for years 

 (in one case, 11 years). Are best formed at 37 C, but 

 also form at 20 C. in 8 to 10 days. 



Habitat. Soil, street dust, horse-dung. 



Pathogenesis. In man : mostly from punctured wounds. 

 The bacillus remains at the local site, but the toxins are 

 carried to the nerve cells of the motor horns of the spinal 

 cord, and of the motor ganglia of the brain. The manner 

 of transmission is believed to be by absorption through 

 the end-plates of the motor nerves in the muscles, and 

 thence via the axis-cylinder processes to the respective 

 nerve cell. The toxins have been shown to have no effect 

 on the motor or sensory endings of the nerves, but solely 

 as an exciter of the nerve cells concerned in reflex action 

 in the cord, pons, and medulla. The affinity of the toxins 

 for the nervous system varies in different animals ; in the 

 guinea-pig it is its chief affinity, whereas in the alligator 

 it shows no affinity, and intermediate degrees exist. 

 Section of a nerve, e.g., the sciatic nerve, followed by 

 injection of the toxins into the muscles supplied by that 

 nerve, prevents the toxins reaching the spinal cord ; but 

 if the nerve below the section be cut out and introduced 

 into. a mouse, the animal will die of tetanus. Similarly, 

 infection of one side of the cord passes, when the dose is 



