Ho 2 



SCIENCE. 



[N. S. Vol. XX. No. 520. 



least chance for transmission. Whatever 

 increase in disease-producing power may 

 be acquitted must be gained under special 

 conditions, one of which is association with 

 other microbes. Thus, if we could conceive 

 of the same streptococcus, originally an in- 

 habitant of the normal throat, as passing 

 on account of some series of accidents 

 through the bodies "r>f a number of scarla- 

 tina patients, this streptococcus might 

 thereby rise temporarily to the level of a 

 serious menace to the throats and perhaps 

 other organs of relatively healthy people. 



Again, certain microbes like B. coli, the 

 pneumococcus and meningococcus may, by 

 living upon catarrhal mucous membranes 

 and passed by case to case, acquire enough 

 temporary pathogenic power to cause local- 

 ized epidemics under favorable conditions. 

 Any advantage thus gained would soon be 

 sacrificed and the microbe return to the 

 normal condition unless a satisfactory 

 mechanism of transmission could be estab- 

 lished. 



It will be seen that there are many prob- 

 lems before the bacteriologist, problems 

 which have something akin to those of the 

 student of races, varieties and species 

 among higher forms of life. These prob- 

 lems must be attacked with the same pa- 

 tience and pertinacity that were exercised 

 by Mendel, Darwin, De Vries and many 

 others in the effort to i ice the rise of new 

 species. 



In dealing with the great problems of 

 pathogenesis and parasitism as applied to 

 the microorganisms in such a summary and 

 hasty manner, and in endeavoring to trace 

 the law of a declining virulence (and hence 

 mortality) and an advancing parasitism, 

 I may have left some doubts in the reader's 

 mind concerning the ultimate value of 

 medicine, preventive and curative, in con- 

 trolling these diseases, since it might be 

 assumed, according to the hypotheses pre- 

 sented, that they would take care of them- 



selves. This impression will, I think, be 

 dispelled by a little further development 

 of the ideas presented. 



The social and industrial development of 

 the human race is continually leading to 

 disturbances of equilibrium in nature, one 

 of whose direct or indirect manifestations 

 is augmentation of disease. In order to 

 avoid this calamity or reduce its force as 

 much as possible we must make special com- 

 pensations or sacrifices to restore or main- 

 tain the normal balance. The more clearly 

 the kind of compensatory action required 

 is foreseen, the more promptly it is put 

 into effect, the less disease there will be. 

 It is the true function of medical science 

 to discover and put into effect those com- 

 pensatory movements which will counter- 

 balance the temporary ill effects of what, 

 for want of a more illuminating term, we 

 call human progress. 



It is largely through the phenomenon of 

 parasitism that nature attempts to restore 

 the equilibrium, and in this microorgan- 

 isms play the most important part. As 

 soon as the individual falls below a certain 

 level he may become the prey of a micro- 

 scopic, or even an ultramicroscopie, world. 

 Hence the importance of bacteriology in 

 medical science. Much has already been 

 done in determining ways and means for 

 the counterbalancing of the ravages of this 

 microscopic world, but science can not rise 

 above natural law, but must work through 

 it. The optimism of the world frequently 

 places science above natural law and be- 

 lieves it capable of correcting any and all 

 excesses of individuals and races. We 

 may be certain that it will never be able 

 to eliminate the factor of parasitism. Its 

 most important work will continue to be to 

 analyze this factor into its minutest details 

 and to devise means by which this analysis 

 may be made useful in turning aside or 

 at least in deadening the shock of disease. 

 Theobald Smith. 



Medical School of Harvard University. 



