412 TETANUS 



the most susceptible regions, the peripheral nerves next, then 

 regions with an abundant nerve supply, such as the face ; and 

 lastly, regions poorly supplied, such as the subcutaneous and 

 peritoneal tissues. The incubation period of tetanus is thus seen 

 to be composed of : (i) the time necessary for the production of the 

 toxin in the tissues ; (2) for its ascent of the nerves to the brain 

 being longer, other things being equal, if infection takes place at 

 a long distance therefrom ; and (3) the latent period which elapses 

 after the toxin has united with the ganglion cells of the central 

 nervous system, and before the development of symptoms i.e., that 

 in which the enzyme-like action of the zymophore group is being 

 gradually exerted on the protoplasm. The fixation of tetanus 

 toxin in the system is extremely rapid: in rabbits it may dis- 

 appear entirely from the blood in one minute, whilst in other 

 susceptible animals it circulates for slightly longer periods. The 

 importance of this arises from the fact that toxin which has once 

 entered the nerves is thereby shielded from the action of antitoxin. 

 The dose of antitoxin necessary to save the life of an animal which 

 has received a few lethal doses of toxin rises enormously if the 

 injection of the former is delayed more than a few minutes. 



Tetanolysin is even more fragile than tetanospasmin, being 

 converted into toxoids in a few hours at the room temperature. 

 It can be preserved in a dry state. The role which it plays in 

 natural infections, if any, is unknown. 



As regards immunity, there is but little to add to what has been 

 discussed previously. The bacilli are not powerful parasites, 

 being readily ingested by the leucocytes, and destroyed if the 

 conditions are favourable for phagocytosis. In most of the cases 

 which develop tetanus there is a contused or lacerated wound, 

 with much killed and bruised tissues and an abundant con- 

 comitant infection with other bacteria, which still further paralyze 

 the natural resistance of the part. These organisms may have 

 an additional influence in securing a condition of anaerobiosis : 

 tetanus bacilli grown in symbiosis with certain other bacteria 

 which have powerful oxygen-absorbing properties will develop 

 vigorously, and develop toxin in spite of the free access of air. 

 No observations with regard to the opsonic index in tetanus 

 appear to have been recorded. The question of immunity to 

 tetanus toxin has been dealt with already, but we may add that 

 in all probability much of the toxin is destroyed in loco by the 

 unspecific action of the peptic enzyme formed by the leucocytes 



