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SCIENCE 



[N. S. Vol. LII. No. 1357 



healthy animal by the direct inoculation of 

 blood containing the anthrax bacillus, the 

 science of bacteriology may be said to have 

 been born. 



The dates are significant to one who wishes 

 to follow the march of events which brought 

 the greatest master of all, Pasteur, into the 

 field of microbiology and led him on to the 

 study of the infectious diseas.es, first of ani- 

 mals and then of man^^-^Ior on looking back- 

 ward we find that coincidental with Davaine's 

 epochal experiments, Pasteur was already en- 

 gaged on those studies of fermentation and 

 putrefaction which were not only to set oiur 

 conception of those processes on a secure bio- 

 logical foundation, but as an important side 

 effect were to demolish, once and forever, the 

 elaborately constructed but insecurely based 

 doctrine of the spontaneous generation of mi- 

 croscopic forms of life. 



For Pasteur it was but a step, although for 

 us one of the highest importance, from the 

 studies in fermentation and putrefaction to 

 those on the infectious diseases in which, in- 

 deed, the great triumphs he achieved consist 

 far less in the detection of new kinds of 

 microbes to which the various contagious dis- 

 eases might be described, than in his funda- 

 mental discoveries in inunimology, or the sci- 

 ence of the specific prevention of disease. 



This work in the field of immunology, first 

 opened to experimental investigation by him, 

 is the aspect of Pasteur's labors to which I 

 wish esi)ecially to direct your attention, since 

 it forms the connecting bond between the 

 earliest and thus the oldest, and the present 

 and thus the latest discoveries in a field in 

 which medical science has come to secure 

 some of its most notable successes. There 

 can be no doubt that the discovery in 1880 of 

 the artificial immunity to fowl cholera came 

 not as a direct incident, but rather as an ac- 

 cidental circumstance to the experiments be- 

 ing pursued. In after years Pasteur loved to 

 point out the importance of the "prepared 

 mind" as a requisite of the investigator, in 

 order that he may seize hold of and utilize 

 in respect to a question propounded by ex- 

 periment what, viewed superficially, appears 



to be only an indirect and misleading answer. 

 The advances leading rapidly from the arti- 

 ficially induced immunity in fowl cholera to 

 the dramatic and historically and economic- 

 ally important immunity in anthrax and to 

 the hmnanly important immunity in rabies, 

 involved no strictly new conceptions on 

 Pasteur's part. They consisted merely of the 

 carrying forward of the ideas, often ingeni- 

 ously modified, derived from the study of the 

 sources of the condition of immunity in fowl 

 cholera. 



But should we inquire to what order of 

 events already known this phenomenon of 

 artificial iromunity belongs, we should say at 

 once probably to the order having to do with 

 the Jennerian vaccination against smallpox. 

 As every one knows, vaccination against 

 smallpox consists in the utilization of human 

 smallpox material which has become modified 

 by passing through the cow, in which it sets 

 up the condition named cowpox. When this 

 modified microbic virus of the disease is re- 

 turned to man, a mild form of smallpox is 

 induced, which suffices through a term of 

 years to protect the individual vaccinated, so- 

 called, from infection with the more active or 

 virulent smallpox virus. 



The significance of the new observations 

 was grasped by Pasteur and related to Jen- 

 nerian vaccination. His great discovery then 

 consisted in the determination that patho- 

 genic or disease-producing microbes may be 

 modified otherwise than by passing through 

 foreign and relatively insusceptible animal 

 species, and that such simple agencies as long 

 cultivation in vitro (fowl cholera), high tem- 

 peratures and therefore non-optimal condi- 

 tions of growth (anthrax), and partial drying 

 of the animal material caiTying the microbe 

 (rabies), would suffice so to modify and at- 

 tenuate the respective microbes that upon in- 

 oculation they set up not the severe, but only 

 mild states of infection, from which not only 

 does recovery ensue, but the restored animal 

 is enduringly protected from the ordinary and 

 often fatal attacks of a disease. 



Looking backward from our present higher 

 position of vantage, we may discern certain 



