Disease Transmission and Mans Resistance 323 



Rabies Vaccine 



When one visits Paris and sees the statues and monuments, he 

 ojets the impression that Louis Pasteur's development of a treat- 

 ment for the prevention of rabies is the contribution most me- 

 moriahzed by his countrymen. 



Because of the relatively long incubation period for rabies, up 

 to eight weeks or more, active immunization can be employed in 

 persons bitten by rabid animals, or by animals suspected of having 

 rabies. The most common technic is the use of Semple vaccine, 

 which is a phenolized preparation of infected rabbit spinal cord. 

 Daily subcutaneous injections of vaccine for a period of fourteen 

 days after exposure will produce active immunity and will usually 

 prevent the development of the disease in humans. 



Rabies is caused by one of the larger viruses, measuring up to 

 250 millimicrons. The etiological agent is transmitted to man 

 through the saliva by bites of dogs, wolves, and vampire bats. 

 Other animals have also been known to carry the virus. The or- 

 ganism has a strong affinity for cells of the central nervous system, 

 and the incubation period before clinical manifestations appear is 

 related to the distance from the brain that the bite is inflicted. 

 Bites around the face generally have a shorter incubation period 

 than bites on the legs or on the arms. 



When an animal suspected of being rabid is sent to the labora- 

 tory for examination to confirm the suspicion, stained sections of 

 the animal's brain are examined under the microscope for char- 

 acteristic granules within certain brain cells. The presence of 

 these Negri bodies confirms the diagnosis of rabies. Once the 

 clinical symptoms appear in humans, the chances for recovery drop 

 off very sharply. 



Bacterins 



A bacterin is a killed culture of bacteria, and when this vaccine 

 is injected into susceptible animals it induces an active immunity. 

 After cultivating the organisms under suitable growth conditions, 

 which sometimes involves growing them in animals (so-called 



