we can hardly expect that a method which is satisfactory in meeting one of the diseases will be very likely to be adapted to another.  Vaccination has proved of value in smallpox, but is not of use in other human diseases.  Inoculation with weakened germs has proved of value in anthrax and fowl cholera, but will not apply to all diseases.  Each of these parasites must be fought by special methods, and we must not expect that a method that is of value in one case must necessarily be of use elsewhere.  Above all, we must remember that the antitoxines do not cure in themselves; they only guard the body from the weakening effects of the poisons until it can cure itself, and, unless the body has resisting powers, the antitoxine will fail to produce the desired results.

One further point in the action of the antitoxines must be noticed.  As we have seen, a recovery from an attack of most germ diseases renders the individual for a time immune against a second attack.  This applies less, however, to a recovery after the artificial inoculation with antitoxine than when the individual recovers without such aid.  If the individual recovers quite independently of the artificial antitoxine, he does so in part because he has developed the antitoxines for counteracting the poison by his own powers.  His cellular activities have, in other words, been for a moment at least turned in the direction of production of antitoxines.  It is to be expected, therefore, that after the recovery they will still have this power, and so long as they possess it the individual will have protection from a second attack.  When, however, the recovery results from the artificial inoculation of antitoxine the body cells have not actively produced antitoxine.  The neutralization of the poisons has been a passive one, and after recovery the body cells are no more engaged in producing antitoxine than before.  The antitoxine which was inoculated is soon eliminated by secretion, and the body is left with practically the same liability to attack as before.  Its immunity is decidedly fleeting, since it was dependent not upon any activity on the part of the body, but upon an artificial inoculation of a material which is rapidly eliminated by secretion.

Conclusion.

It is hoped that the outline which has been given of the bacterial life of Nature may serve to give some adequate idea of these organisms and correct the erroneous impressions in regard to them which are widely prevalent.  It will be seen that, as our friends, bacteria play a vastly more important part in Nature than they do as our enemies.  These plants are minute and extraordinarily simple, but, nevertheless, there exists a large number of different species.  The number of described forms already runs far into the hundreds, and we do not yet appear to be approaching the end of them.  They are everywhere in Nature, and their numbers are vast beyond conception.  Their powers of multiplication are inconceivable,