﻿10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 59 



With factors so various, it is obvious that conditions which cannot 

 always be followed must make for and against infection. This is 

 the element in the problem that is popularly termed " chance " ; and 

 yet this audience need not be told that the term is a mere euphemism 

 for ignorance. Coincidences and probabilities are among the common 

 factors of infection. It is not chance, but ignorance or indifference 

 that carries a free person into a plague infested region; and once 

 there it is fleas and not chance that decide whether he shall or shall 

 not acquire plague. No more is it chance, but only augmented sus- 

 ceptibility, that causes one disease to play into the hands of another, 

 and that decides that the victim of measles, scarlet fever, or small- 

 pox shall succumb to a streptococcal pneumonia or blood infection 

 to which those diseases render him morbidly liable ; and no more is 

 it chance that the bearer of a severely damaged heart or kidney or 

 liver shall finally be overcome by a terminal bacterial infection. What 

 the flea has determined for the plague, the diseases predisposing to 

 infection with the pus-producing bacteria accomplish by damaging 

 the body's external and internal defenses against this ubiquitous class 

 of microbic parasites, that ever lurk about seeking opportunity to in- 

 vade and propagate within the blood and tissues. 



So, as we have seen, medicine has advanced from empiricism and 

 become scientific, as chemistry and physics have advanced from al- 

 chemy, and astronomy from astrology, and become scientific, by rigid 

 experimental investigation and controlled, logical observation, until 

 now the domain of knowledge is differentiated from the domain of 

 ignorance and superstition by a vigorous body of ascertained truths 

 and established methods of research that rest neither on authority 

 nor opinion. The tangible gains have been such perfected means of 

 combating disease as are represented by the specific serums that have 

 reduced the mortality from diphtheria and epidemic meningitis to 

 one-fourth of the spontaneous recovery rates, the dangers from 

 tetanus and hydrophobia from infected wounds, by means of protec- 

 tive injections, almost to zero, and through preventive inoculation 

 the liability to typhoid fever to a vanishing figure. And thus it has 

 also been achieved that the discovery of specific chemical means of 

 suppressing disease is no longer left to the heart-breaking method of 

 finding useful drugs, in the manner that quinine and mercury were 

 found, by an infinite series of tests upon suffering human beings, 

 based upon pure accident, "but by following ascertained clues, first in 

 the laboratory upon the lower animals, until by a process of selection 

 and perfection, such remarkable instruments for the control of ser- 

 ious diseases as salvarsan shall have been evolved. 



