528 GrENERAL DISEASES. 



become virulent and produce tetanus. Hence, the fact that, occasionally, the 

 period of incubation is unusually long. The conditions in question appear to be 

 those which diminish -the resistance of the tissues, by repelling the protective 

 leucocytes ; one of the chief of these conditions being the presence of certain 

 common microbes which produce pus and wliich favour the development of 

 the micro-organisms of tetanus, (Suppurating wounds are therefore particu- 

 larly good breeding grounds for the bacilli of this disease. Injury and the 

 presence of foreign bodies also act favourably in the same direction. Hence, 

 A\'e find that wounds which become polluted with soil and dirt are speci- 

 ally liable to be followed by symptoms of tliis disease; and the lesson is 

 obvious that the cleaner we keep wounds, the less danger will there be of 

 tetanus. 



It appears that the skin and mucous membrane, when unbroken and in a 

 healthy state, will bar the entrance, into the system, of the tetanus poison, 

 wliich, however, is capable of getting through the smallest breach existing 

 in these coverings. Before the nature of the disease was known, cases in 

 wliich a wound was evidently the point of infection were classed as those of 

 " traumatic tetanus ; " and cases in which no wound was discernible, as 

 those of "idiopathic tetanus." Such a distinction is, witli our present 

 state of knowledge, not alone unnecessary, but is misleading. As these bacilli 

 cannot develop in air (or rather in oxygen), punctured wounds are more 

 favourable to the production of tetanus than superficial ones. Also, as there 

 is a fair amount of oxygen in the blood, these microbes caimot live in it, 

 unless when it has lost a large proportion of its oxygen, and consequently 

 they remain, as a rule, in more or less close proximity to their original point 

 of entrance. The fact that the microbes of this disease very rarely indeed 

 obtain entrance from accidentally-inflicted clean-cut wounds, is probably 

 owing to the comparative freedom from contamination enjoyed by these 

 injuries. No such immunity is possessed by clean-cut wounds made by 

 surgical instruments which have been employed in tetanus cases, and which 

 have not been thoroughly disinfected. These germs are frequently found in 

 some districts, and rarely in others. They appear to be much more common 

 in the tropics than in temj)erat6 climates. Nicolaier proved that the sub- 

 cutaneous inoculation of earth often gave rise to tetanus. In such cases it is 

 almost needless to say that the inoculated earth contained the spores of this 

 disease and other mioro-organisms which are favourable to their development. 

 We should, therefore, be particularly careful to clean and thoroughly disinfect 

 all wounds^suoh as broken knees, overreaches, and especialy punctured sole 

 and frog — whidh are liable to contamination from the soil. 



Bonome and other observers have proved that the microbes of tetanus, when 

 in the form of spores, can j)reserve their vitality even in boiling water. The 

 poison of tetanus can be destroyed by strong acids, like carbolic acid or 

 hydrochloric acid, by boihiig water, or by keeping it for five minutes at a 

 temperature of 130'^ F. Hence, it does not appear dangerous to allow animals 

 (hounds, for instance) to consume the cooked flesh of horses which have died 

 of tetanus. Dogs are much less susceptible to it than are horses. Hewlett 

 states that direct sunlight destroys it in from fifteen to eighteen hours' expo- 

 sure ; and that it maintains its virulence almost indefinitely in a cool dark place. 

 These considerations and the fact that tetanus germs cannot develop in air, 

 teach us the advisability, in the prevention of this and other diseases, of 

 exposing, as much as practicable, the bedding of our horses, and the interior 

 of our stables, to the purifying action of sunlight and fresh air. 



Tetanus, as we have seen, can occur only by inoculation. For all practical 

 purposes, we may accept as a fact that one horse cannot give it to another ; 

 although it might very easily be conveyed by an intennediate carrier, such as 

 the hands or instruments of a person who had been attending a case of 

 tetanus. It is probable that when the disease follows a surgical operation, 

 the poison has been derived, as a rule, from infected instruments. The wounds 

 which are most generally followed by lockjaw, 'are those of castration, dock- 

 ing, broken knees, deep wounds in a limb, and especially punctures in a foot. 



