MICROBIAL DISEASES OF MAN AND ANIMALS. 639 



cultures a pine tree growth occurs. Gas is usually produced. In milk growth occurs 

 without coagulation. Acid is produced in some carbohydrate media. Gas is produced 

 during the action upon protein and consists chiefly of carbon dioxide but also of 

 hydrogen sulphide and certain volatile organic compounds commonly found in putre- 

 factions. The tetanus bacillus forms two soluble toxins, tetano-lysin, and tetano- 

 spasmin. The former is less stable and dissolves red blood-corpuscles. The latter 

 produces the characteristic spasms of the muscles. This poison may be obtained 

 after one to two weeks growth in slightly alkaline salt-peptone-bouillon under 

 anaerobic conditions at 37.5 and separated by filtration through porcelain filters. 

 When taken by the mouth the toxin is ineffective, given intravenously it produces a 

 generalized tetanus, while after subcutaneous injection the disease begins with local 

 spasms. The central nervous system is reached by ascent of the toxin along the 

 motor nerves nearest the point of inoculation. A dose of toxin injected directly into 

 the nerve trunk of an animal may produce a fatal result when it is innocuous intra- 

 venously. The spores often withstand 80 for one hour and live steam for about ten 

 minutes. Direct sunlight destroys them in time. They survive drying for several 

 years and resist the ordinary disinfectants for a considerable length of time, 1:1000 

 mercuric chloride for three hours, 5 per cent carbolic acid for about ten hours. 



Practically all mammalia are susceptible to tetanus though rats are but 

 slightly so. Very minute doses of toxin suffice to kill mice and guinea 

 pigs. Birds show but little susceptibility and the hen is said to be three 

 hundred thousand times more resistant to tetanus toxin than the horse. 

 Reptiles and amphibians are practically immune to very large doses 

 when kept at low temperature. 



Natural infections probably do not occur without the presence of 

 other microorganisms. The bacillus and its associated material gains 

 entrance through some break in the tissues. The organism is practically 

 confined to the site of inoculation, but it is sometimes found in the 

 blood and internal organs after death. 



Against toxin-freed cultures phagocytosis is probably the process 

 which overcomes infection. The toxin is highly antigenic and animals 

 can be immunized against it in a manner similar to that for diphtheria 

 toxin. 



While direct infection of one person from another has occurred, cases 

 of human tetanus are very rarely responsible for others. 



Horses are chiefly responsible for its distribution, the tetanus bacillus 

 being common in manure, which accounts for the occurrence of tetanus 

 in soil-contaminated injuries. 



Cattle probably are also carriers of the bacillus. Tetanus antitoxin 

 as a cure has been a keen disappointment, especially if symptoms have 



