98 DISEASES OF 



" punctured foot," caused usually by "picking up nails." 

 It is also caused by a germ. The reason that it so often 

 follows punctured wounds is that the entrance of 

 air into such wounds is prevented by the walls of the 

 wound immediately closing. Investigations have re- 

 cently discovered that the germ that causes lock-jaw 

 cannot grow and propagate if exposed to the air ; but 

 if plante I in suitable material and air be excluded, it 

 thrives and is propagated with rapidity. This germ, 

 when growing, generates an intensely active poisonous 

 substance, having much the same properties as strych- 

 nine. This poison is absorbed into the system, and, 

 acting on the central nervous system, causes the pecu- 



Fig. 33. Appearance of horse suffering from Lockjaw 



