324 



Constant 



fell ill; they seemed to be immune or not 

 susceptible (suss-sep'ti-ble) to the dis- 

 ease. In those days the various antibodies 

 had not yet been recognized, but Pas- 

 teur knew that in some way the animal 

 must be responding to the bacteria. 



Could he make animals immune to 

 other diseases? Pasteur turned his atten- 

 tion to anthrax. He decided to try to 

 weaken the germs in a new way, by sub- 

 jecting them to a high temperature 

 (io8° F) for some days; this proved suc- 

 cessful. When he injected such germs 

 into healthy sheep, the animals con- 

 tracted anthrax, but in a mild form. 

 When the sheep had recovered entirely 

 from that attack, he inoculated them 

 with the most virulent (strongest) an- 

 thrax germs he could find. Most of the 

 animals had become completely immune 

 to the disease; just a few had a slight at- 

 tack of anthrax. Since the tissues of the 

 sheep had been active in making anti- 

 bodies we say that the sheep had devel- 

 oped active iimmmity against anthrax. 



Scientists were so skeptical that Pas- 

 teur was obliged to give a public demon- 

 stration of his work. Even then there 

 were many who refused to believe that 

 by giving a disease one could prevent 

 the development of that disease later on. 



Pasteur inoculates against rabies. Hav- 

 ing been so successful in immunizing 

 animals against two diseases, Pasteur at- 

 tempted to apply the same principle to 

 hydrophobia, or rabies (ray'bees). For- 

 merly, rabies was a common disease 

 among dogs and from them it frequently 

 spread to human beings and some other 

 animals. It was always fatal. After much 

 experimentation, Pasteur succeeded in 

 weakening the organism which caused 



Care Is Needed for Health unit vi 



rabies although he never was able to see 

 it. It is believed now to be one of the 

 filterable viruses (vy'rus-es), one of the 

 organisms too small to be seen with the 

 ordinary microscope. Pasteur suspected 

 that the organism settled in the spinal 

 cord and brain. So he cut out the spinal 

 cord of a rabbit which had died of ra- 

 bies. By drying the spinal cord he suc- 

 cessfully weakened the virus. When he 

 injected this weakened virus into dogs, 

 starting with the weakest virus (mate- 

 rial that had been dried the longest time) 

 and using stronger doses with each inoc- 

 ulation he found that the dogs became 

 immune to rabies. 



Although the experiments had all been 

 successful and the theory underlying 

 them seemed sound, Pasteur still hesi- 

 tated to try out his weakened virus on 

 human beings. One day he was obliged 

 to do so. A nine-year-old boy who had 

 been bitten by a mad dog was brought 

 to his laboratory. The parents pleaded 

 with Pasteur to use his treatment on the 

 child. Still Pasteur hesitated, for this case 

 was different from those he had experi- 

 mented with before. In his laboratory 

 dogs had been inoculated with the virus 

 before they had been bitten by a rabid 

 animal. Now he was asked to inject virus 

 into the child which had already been 

 bitten. Knowing that the disease comes 

 on very slowly, sometimes many, weeks 

 after the bite, he thought that possibly 

 the inoculations could take effect in time 

 to save the child. Knowing too that with- 

 out treatment the child could not pos- 

 sibly recover, Pasteur finally yielded to 

 the persuasion of the parents. After four- 

 teen days of treatment the child left the 

 hospital; rabies never developed. 



