IMMUNITY AGAINST TETANUS. 389 



which have been accidentally subjected to conditions such as 

 those enumerated. Kitasato now holds that in the natural 

 infection in man, along with tetanus spores, the presence of 

 foreign material or of other bacteria is necessary. Spores alone 

 or tetanus bacilli without spores die in the tissues, and tetanus 

 does not result. 



Summary. In view of all the facts available we must thus 

 look on tetanus as caused by the B. tetani. The bacillus gains 

 entrance to the body through wounds or abrasions, and, multi- 

 plying locally, produces poisons which diffuse into the tissues 

 and have an elective action as stimulators, especially of the 

 spinal cord. The chemical composition of these poisons is not 

 yet fully known. The enormous potency of such poisons explains 

 how, even in a fatal case, extreme smallness of the wound and 

 difficulty in isolating the bacillus do not detract from the theory 

 that the latter is the cause of the disease. 



Immunity against Tetanus. Antitetanic Serum. The arti- 

 ficial immunisation of animals against tetanus has received 

 much attention. The most complete study of the question is 

 found in the work of Behririg and Kitasato in Germany, and of 

 Tizzoni and Cattani in Italy. The former observers found that 

 such an immunity could be conferred by the injection of very 

 small and progressively increasing doses of the tetanus toxin. 

 The degree of immunity attained, however, was not high. 

 More successful was the method of accompanying the early 

 injections of such toxin with the subcutaneous introduction of 

 small doses of iodine terchloride. Tizzoni and Cattani have also 

 used the method of administering progressively increasing doses 

 of living cultures attenuated in various ways, e.g. by heat. By 

 any of these methods susceptible animals can rapidly acquire 

 great immunity, not only against many times the fatal dose of 

 tetanic toxin, but also against injections of the living bacilli. The 

 degree of immunisation acquired by an animal remains in exist- 

 ence for several months. Not only so, but when a high degree 

 of immunity has been produced by prolonged treatment, it is 

 found that the serum of immune animals usually possesses the 

 capacity, when injected into animals susceptible to the disease, 

 of protecting them against a subsequent infection with a fatal 

 dose of tetanus bacilli or toxin. Further, if injected subse- 

 quently to such infection, the serum can in certain cases prevent 



