[246 Mothers’ remedies]

This he accomplished after many experiments.  He proved that pieces of the “medulla oblongata” suspended in sterile tubes which contained fragments of caustic potash, steadily and gradually reduced their virulence as they dried, till the fourteenth day, when they were practically inert.  New specimens were prepared each day and cords which had dried in one day Pasteur called “one-day virus;” cords which had dried in two days, “two day’s virus,” and so on up to the fourteenth day.  With this graduated virus he now experimented on dogs, and the injection he used on the first day consisted of an emulsion of fourteen-day virus; for the second day, the thirteen-day virus, thus using a stronger virus each day, until on the fourteenth day he used the full strength virus.  This treatment produced what is called immunity in the dog, and even the direct inoculation into the brain of the strong virus would not produce death.

After Pasteur had thoroughly satisfied himself by repeated trials, he announced his wonderful discovery, and it was in 1886 that Pasteur considered the preventive inoculation in human beings as resting upon a satisfactory experimental basis.  During these five years this eminent man proved that it was possible to protect or immunize the lower animals, rabbits and dogs, against inoculation with the virulent virus.

The efficiency of this immunity was given trials by different methods of inoculation.  It was found that sixty per cent of dogs inoculated under the “dura” (a membrane of the brain) were saved if treatment was given the second day.  This test is more severe than is required to meet the ordinary infection of rabies.  Pasteur, after a series of these final tests were so convincing, prescribed the preventive inoculations in human beings and on July 6th, 1886, the first human patient received the first treatment of his series of inoculations.

The method of obtaining the attenuated virus used in the treatment is as follows:  A rabbit is inoculated by the brain method before described, each day, with suspension of the fresh, fixed virus.  These rabbits die in six days after the inoculation.  In this way a rabbit dies each day; the spinal cord is removed, divided into sections, and suspended in a flask containing potassium hydrate.  The action of potassium hydrate is drying (desiccating).  A series of these cords, which have been hung on fourteen successive days, are always kept in stock for the treatment of patients.  The virus becomes less active with each successive day of exposure to drying (desiccation) and finally the virulence is altogether lost.

When the patient comes for treatment the fourteenth and thirteenth-day cords are used for the first inoculation, and on each successive day the patient receives inoculation, the strength of which has been regulated by the number of days the cord has been hanging.  During the first four days patients receive injections of six cubic centimeters of emulsions made from cords aging from fourteen to seven days, and from the fifth day until the completion of the course of treatment patients receive emulsions from cords of higher immunizing properties, but no cords desiccated for less than four days are used.