But why should not a germ disease be always fatal?  If the bacteria thus take possession of the body and can grow there, why do they not always continue to multiply until they produce sufficient poison to destroy the life of the individual?  Such fatal results do, of course, occur, but in by far the larger proportion of cases recovery finally takes place.

Plainly, the body must have another set of resisting forces which is concerned in the final recovery.  Although weakened by the poisoning and suffering from the disease, it does not yield the battle, but somewhat slowly organizes a new attack upon the invaders.  For a time the multiplying bacteria have an unimpeded course and grow rapidly; but finally their further increase is checked, their vigour impaired, and after this they diminish in numbers and are finally expelled from the body entirely.  Of the nature of this new resistance but little is yet known.  We notice, in the first place, that commonly after such a recovery the individual has decidedly increased resistance to the disease.  This increased resistance may be very lasting, and may be so considerable as to give almost complete immunity from the disease for many years, or for life.  One attack of scarlet fever gives the individual great immunity for the future.  On the other hand, the resistance thus derived may be very temporary, as in the case of diphtheria.  But a certain amount of resistance appears to be always acquired.  This power of resisting the activities of the parasites seems to be increased during the progress of the disease, and, if it becomes sufficient, it finally drives off the bacteria before they have produced death.  After this, recovery takes place.  To what this newly acquired resisting power is due is by no means clear to bacteriologists, although certain factors are already known.  It appears beyond question that in the case of certain diseases the cells of the body after a time produce substances which serve as antidotes to the poisons produced by the bacteria during their growth in the body-antitoxines.  In the case of diphtheria, for instance, the germs growing in the throat produce poisons which are absorbed by the body and give rise to the symptoms of the disease; but after a time the body cells react, and themselves produce a counter toxic body which neutralizes the poisonous effect of the diphtheria poison.  This substance has been isolated from the blood of animals that have recovered from an attack of diphtheria, and has been called diphtheria antitoxine.  But even with this knowledge the recovery is not fully explained.  This antitoxine neutralizes the effects of the diphtheria toxine, and then the body develops strength to drive off the bacteria which have obtained lodgment in the throat.  How they accomplish this latter achievement we do not know as yet.  The antitoxme developed simply neutralizes the effects of the toxine.  Some other force must be at work to get rid of the bacteria, a force which can only exert itself after the poisoning effect of the poison is neutralized.  In these cases, then, the recovery is due, first, to the development in the body of the natural antidotes to the toxic poisons, and, second, to some other unknown force which drives off the parasites.