PATHOGENESIS INFECTION. 231 



tubes are inoculated with the material containing the tetanus 

 bacillus and placed in the incubator for two days. This will 

 cause the development of not only the tetanus bacillus, but 

 also of all other organisms contained in the culture. This 

 mixed culture is heated on a water-bath at a temperature of 

 80 C. for one hour. This destroys all the bacteria, including 

 the tetanus bacillus, but does not affect the spores of the latter. 

 Pure cultures are made from this spore-containing culture 

 according to the methods previously described for the cultiva- 

 tion of anaerobic bacteria. 



Pathogenesis : Man and nearly all the domestic animals, 

 except dogs and birds, are susceptible to tetanus. The infec- 

 tion, in order to become manifest, must take place through a 

 wound. The organism is a very common saprophyte in the 

 soil, and cattle, when feeding on grass, are quite liable to 

 swallow the germ, which passes through the gastro-intestinal 

 tract without exhibiting any evidence of infection. The fact 

 that the tetanus bacillus is so frequently found in manure 

 proves that it may be ingested by animals without producing 

 the disease. It grows luxuriantly in jnanured ground. Teta- 

 nus can also be produced artificially by injecting the germ 

 into the circulation or into the peritoneal or other cavities. 



Infection : The most frequent portal of entry of the germ is 

 through the skin. Usually the site of infection is easily recog- 

 nized, but occasionally cases of tetanus are seen in which it is 

 impossible to find any evidence of an injury which may have 

 served as an infection atrium. Penetrating wounds offer the 

 most suitable lodgement for the bacillus. Stepping on a rusty 

 nail or the prongs of a pitchfork or garden-rake are well- 

 known methods of infection in tetanus, or lock-jaw, as the 

 disease is designated by the laity. It was at one time believed 

 that tetanus was the inevitable result of such an injury. The 

 wound may, however, be produced by any other object than 

 those mentioned. Neither is it essential that the nail or prong 

 be rusty, although the danger of infection in that case is much 

 greater, as the rusty nail has lain on the ground for some time, 

 and is more liable to be the " host " of the tetanus bacillus 

 than a clean nail. 



The wire wrapped around baled hay is also responsible 



