as to make people in general willing to submit to inoculation as a protection.  A further objection arises from the fact that the immunity acquired is not necessarily lasting.  The cattle inoculated against anthrax retain their protective powers for only a few months.  How long similar immunity might be retained in other cases we can not say, but plainly this fact would effectually prevent this method of protecting mankind from being used except in special cases.  It is out of the question to think of constant and repeated inoculations against various diseases.

As a result, the principle of inoculation as an aid in preventive medicine has not proved of very much value.  The only other human disease in which it has been attempted seriously is Asiatic cholera.  This disease in times of epidemics is so severe and the chance of infection is so great as to justify such inoculation.  Several bacteriologists have in the last few years been trying to discover a harmless method of inoculating against this disease.  Apparently they have succeeded, for experiments in India, the home of the cholera, have been as successful as could be anticipated.  Bacteriological science has now in its possession a means of inoculation against cholera which is perhaps as efficacious as vaccination is against smallpox.  Whether it will ever be used to any extent is doubtful, since, as already pointed out, we are in a position to avoid cholera epidemics by other means.  If we can protect our communities by guarding the water supply, it is not likely that the method of inoculation will ever be widely used.

Another instance of the application of preventive inoculation has been made, but one based upon a different principle.  Hydrophobia is certainly one of the most horrible of diseases, although comparatively rare.  Its rarity would effectually prevent mankind from submitting to a general inoculation against it, but its severity would make one who had been exposed to it by the bite of a rabid animal ready to submit to almost any treatment that promised to ward off the disease.  In the attempt to discover a means of inoculating against this disease it was necessary, therefore, to find a method that could be applied after the time of exposure—­i.e., after the individual had been bitten by the rabid animal.  Fortunately, the disease has a long period of incubation, and one that has proved long enough for the purpose.  A method of inoculation against this disease has been devised by Pasteur, which can be applied after the individual has been bitten by the rabid animal.  Apparently, however, this preventive inoculation is dependent upon a different principle from vaccination or inoculation against anthrax.  It does not appear to give rise to a mild form of the disease, thus protecting the individual, but rather to an acquired tolerance of the chemical poisons produced by the disease.  It is a well-known physiological fact that the body can become accustomed to tolerate poisons if inured