The result has been a complete revolution in surgery.  As the methods have become better understood and more thoroughly adopted, the instances of secondary troubles following surgical wounds have become less and less frequent until they have practically disappeared in all simple cases.  To-day the surgeon recognises that when inflammatory troubles of this sort follow simple surgical wounds it is a testimony to his carelessness.  The skilful surgeon has learned that with the precautions which he is able to take to-day he has to fear only the direct effect of the shock of the wound and its subsequent direct influence; but secondary surgical fevers, blood poisoning, and surgical gangrene need not be taken into consideration at all.  Indeed, the modern surgeon hardly knows what surgical gangrene is, and bacteriologists have had practically no chance to study it.  Secondary infections have largely disappeared, and the surgeon is concerned simply with the effect of the wound itself, and the power of the body to withstand the shock and subsequently heal the wound.

With these secondary troubles no longer to disturb him, the surgeon has become more and more bold.  Operations formerly not dreamed of are now performed without hesitation.  In former years an operation which opened the abdominal cavity was not thought possible, or at least it was so nearly certain to result fatally that it was resorted to only on the last extremity; while to-day such operations are hardly regarded as serious.  Even brain surgery is becoming more and more common.  Possibly our surgeons are passing too far to the other extreme, and, feeling their power of performing so many operations without inconvenience or danger, they are using the knife in cases where it would be better to leave Nature to herself for her own healing.  But, be this as it may, it is impossible to estimate the amount of suffering prevented and the number of lives saved by the mastery of the secondary inflammatory troubles which used to follow surgical wounds.

Preventive medicine, then, has for its object the prevention rather than the cure of disease.  By showing the causes of disease and telling us where and how they are contracted, it is telling us how they may to a large extent be avoided.  Unlike practical medicine, this subject is one which has a direct relation to the general public.  While it may be best that the knowledge of curative methods be confined largely to the medical profession, it is eminently desirable that a knowledge of all the facts bearing upon preventive medicine should be distributed as widely as possible.  One person can not satisfactorily apply his knowledge of preventive medicine, if his neighbour is ignorant of or careless of the facts.  We can not hope to achieve the possibilities lying along this line until there is a very wide distribution of knowledge.  Every epidemic that sweeps through our communities is a testimony to the crying need of education in regard to such simple facts as the source of infectious material, the methods of its distribution, and the means of rendering it harmless.