282 THE PRINCIPLES OF IMMUNOLOGY 



durability of the immunity produced by vaccination are inaccurate. 

 In order to secure satisfactory immunity, vaccination should be re- 

 peated at intervals of a few years. In those communities where small- 

 pox is endemic vaccination should be repeated every year. In the 

 presence of epidemics, an unsuccessful vaccination should not be inter- 

 preted as indicating immunity and should be repeated at intervals of a 

 week or ten days until successful. We feel that no dependence can 

 be unqualifiedly placed on the signs of immunity as indicated by 

 Force (page 243). 



Unfavorable Results of Vaccination. If human virus be employed 

 the chance of inoculating syphilis must be considered, although the 

 danger is slight. Reports of tetanus following shortly after vaccina- 

 tion have not been particularly well founded and examination of a 

 large number of samples collected by the Hygienic Laboratory in 

 Washington by McCoy and Bengston failed to demonstrate the pres- 

 ence of the bacilli or their spores in filled capillary tubes, seed vaccine 

 or in bulk glycerolated vaccine. " Ivory points " were found to be 

 contaminated as delivered from the manufacturer of the points, as well 

 as after sterilization and charging. McCoy states that " the sale of 

 vaccine virus on or with points in interstate traffic has been prohibited 

 by an order of the Secretary of the Treasury." 



The most important source of trouble is the result of vaccination in 

 unclean skin, the use of unclean dressings or other failures of asepsis, 

 more particularly those resulting from carelessness on the part of the 

 patient. Such infections usually remain localized but confuse the 

 interpretation of results and may in rare instances become gen- 

 eral infections. 



Vaccination Against Rabies. The cause of rabies is probably a 

 sporozoan parasite discovered by Negri and named by Calkins " neuro- 

 ryctes hydrophobise." Work with this parasite is difficult because of 

 failure to isolate the organism in suitable form. Therefore, the investi- 

 gations have been conducted with pathological material containing the 

 organism. It is found in greatest amounts in tjie nervous system and 

 accordingly the brain or cord is selected for experimental work. This 

 material is spoken of as the virus of rabies. Street virus is nerve 

 tissue obtained from an animal suffering with the natural disease. It 

 is extremely variable in virulence, and for this reason is not employed 

 for vaccination of man. Fixed virus is usually the spinal cord of 

 rabbits obtained after a long series of rabbit passages. By these animal 

 passages the virulence increases and the incubation period decreases 

 until a point is reached when the incubation period following inocula- 

 tion cannot be further shortened. All mammals are susceptible to rabies 

 in different degrees, but birds or reptiles are not susceptible. 



The treatment of rabies in man after it has developed has been 

 entirely unsatisfactory by the methods of immunology. Immunization 

 of animals to the rabies virus produces an immune serum capable of 

 killing the virus. Accordingly it was hoped that such a serum could 



