MANUFACTURE OF VACCINES 567 



disease is killed and a small portion of the brain removed. The brain 

 tissue is emulsified in sterile water or salt solution and a few drops of the 

 material thus suspended in liquid, are injected subdurally into a rabbit. 

 This may easily be accomplished by trephining the skull, after anaesthe- 

 tizing the animal, and with a small syringe inoculating a few drops of 

 the suspension just under the exposed dura mater. The inoculation of 

 ordinary rabies virus usually produces symptoms of "dumb rabies" 

 and the death of the animal in fourteen to eighteen days. In order to 

 increase the virulent properties of the same strain of rabid material, it 

 is transmitted from rabbit to rabbit by subdural inoculations until 

 the incubation period is sliortened to about six days. Experience has 

 shown that when the virus has reached its maximum degree of virulence 

 for the rabbit, the animal shows symptoms on the sixth or seventh 

 day after inoculation. When the virus attains this degree of virulence 

 it is called "fixed virus" and may be used in the preparation of the 

 vaccine. The "fixed virus" or spinal cord of the rabbit which has 

 succumbed to the disease in six or seven days, is removed aseptically 

 and placed in a special dr)dng chamber. The cords are suspended over 

 caustic potash and dried at a temperature of 23° for a period of from 

 one to ten or fifteen days. 



The treatment of the patient consists in the hypodermic appUca- 

 tion of the "fixed virus" which has been attenuated by drjring. The 

 exact natiure of the vaccine used in the initial vaccination and the time 

 consumed in the series of injections depend, to some extent, upon the 

 case in hand. Frequently, the patient is first vaccinated with a sus- 

 pension of a spinal cord which has been attentuated by drying for four- 

 teen or fifteen days. On the succeeding days of the treatment use is 

 made of the suspension of spinal cords, which have been less and less 

 attenuated. The treatment usually lasts about twenty days or until 

 the patient has received an injection of the least attenuated "fixed 

 virus." 



It is very important, when one is bitten by a rabid animal, that the ' 

 Pasteur treatment be begun as early as possible, in order that active 

 immunity may be secured before the expiration of the incubation period. 

 In many of the larger cities of the United States, for some time, labora- 

 tories have been maintained for the purpose of administering the 

 Pasteur treatment. More recently, commercial laboratories have 



