August 5, 1921] 



SCIENCE 



107 



consider them surviving types. It would seem 

 that where two or more parasites follow the 

 same route and multiply in the same tissues a 

 certain competition tends to eliminate one or 

 the other. If two closely related types exist 

 they rarely multiply in the same host at the 

 same time. Such competitive elimination 

 would leave a divergent assortment of para- 

 sitic organisms and resulting diseases, none 

 of which would be an exact copy of the other. 

 In this case the working out of one cycle does 

 not necessarily enable us to predict what an- 

 other would be. They must each and all be 

 studied individually. 



In this dilemma we may gain assistance 

 from a study of parasitisms in those remote 

 and isolated regions which have not yet been 

 seeded by the white man's diseases, where the 

 prevailing maladies may still be " pure lines," 

 rather than mixtures and combinations. An- 

 other source of material are the many charac- 

 teristic parasitisms of animal life, notably 

 of the mammals and birds. Comparative pa- 

 thology may furnish us with that information 

 which experimental pathology finds it impos- 

 sible to produce. Taking all the diseased and 

 abnormal states due to living agents in man 

 and the higher animals together, a series may 

 be established which fills in many gaps and 

 which may furnish the suggestions and clues 

 needed to bring about a better insight into the 

 dynamic relations between host and parasite. 

 Only through the cooperation of comparative 

 and experimental methods may we hope to 

 gain enough general underlying concepts to 

 explore with some show of rationality new dis- 

 eases successfully. Since science is valued 

 in proportion to its capacity to predict suc- 

 cessfully certain events, medical science will 

 be judged by the way it takes hold of a new 

 phenomenon to determine its etiological ante- 

 cedence. If, in the course of its development, 

 it has failed to take cognizance of factors 

 necessary to build the science into a consistent 

 whole, it should retrace its steps and make up 

 the deficiency. 



Parallel with the continued analysis of phe- 

 nomena there should be another process go- 

 ing on to simplfy the complexity resulting 



from the former and to bring the results of 

 scientific inquiry more or less within the 

 reach of everyday life. What is needed is a 

 synthesis of the many data resulting from 

 analytic study of phenomena. Perhaps I can 

 make myself clearer by using as an illustra- 

 tion some recent investigations. If we ex- 

 amine the various diseases in which the virus 

 is conveyed by insects and arachnids, we shall 

 find that many of the data pertaining to the 

 dissemination of the virus had been accurately 

 worked out before the mode of transmission 

 was discovered. There was lacking, however, 

 a something to harmonize and coordinate 

 them. When the insect carrier was defined 

 these various discrete, apparently unrelated 

 data fell into line. Here was a synthesis 

 which not only substantiated older observa- 

 tions but it enabled the scientist to use the 

 deductive method to develop new inquiries and 

 thereby lift the subject up to a higher level 

 for further analysis. For some years we had 

 knovm that a certain disease of young turkeys, 

 due to the invasion of the tissues through tlie 

 intestinal tract by a protozoan parasite, could 

 be prevented by raising these birds away from 

 older turkeys and common poultry and on soil 

 uncontaminated by them. The explanation 

 came through the discovery that a common 

 worm of these species was needed to injure 

 the mucous membrane and thereby open the 

 way for the protozoan parasite. The nematode 

 also accounted for certain disturbances in the 

 application of the above rules in the rearing 

 of these birds. It synthesized, in other 

 words, the accumulated data. 



With the aid of these illustrations it is pos- 

 sible to understand, at least in part, what must 

 have been the effect of the rapid discovery of 

 various living agents in the eighties of the 

 last century on the medical mind of the 

 period. Many apparently unrelated data sud- 

 denly moved into line and assumed definite 

 relations to one another. The discoveries per- 

 taining to acquired resistance to disease in- 

 volving the action of antitoxins, agglutinins, 

 precipitins and the like have not had as yet 

 the desired eiiect of synthesizing the concep- 

 tion of immunity, because they may be ac- 



