Deoembee 31, 1920] 



SCIENCE 



619 



of diphtlieria and tetanus, and discovered 

 serum therapy. The day for speculation on 

 what constituted ■ the immune state had now 

 definitely passed, and the time had arrived for 

 subjecting the phenomenon to experimental 

 study. 



The fluids or " humors " of the body, to em- 

 ploy a term made respectable by age, as repre- 

 sented by the serum of the blood, had been 

 shown to carry the immunity principles, but 

 what part did the cells of the body play in 

 the process? Both flilids and cells were now 

 submitted to rigid and ingenious scrutiny, 

 and about them an immense literature has 

 grown up. Soon the students in the field 

 divided into two camps, namely, one led by 

 Ehrlich, defending the humoral doctrine, the 

 other led by Metchnikoff, urging the cellular 

 or phagocytic doctrine. The conflicts which 

 raged about these concepts were always ani- 

 mated and sometimes even bitter; but the 

 ultimate effect was to extend rather than to 

 retard and confound knowledge. We are 

 moving now in more peaceful times, the heat; 

 of the earlier conflicts having largely subsided, 

 and it may be stated that neither the one nor 

 the other doctrine finally triumphed, but that 

 the humors or fluids of the body on the one 

 hand and the cells on the other have come to 

 be recognized as the active participating fac- 

 tors in the immunity process, the one com- 

 plementing the other. Where the phenomenon 

 is one purely of the neutralization of a poison 

 or toxin, the fluid portion of the blood suffices ; 

 where also the process is relatively the simple 

 one of acting on and dissolving a bacterial 

 cell, there also the fluid may suffice, although 

 an essential element in the process may have 

 been supplied by the white blood cells at the 

 moment of their withdrawal from the body. 

 But where the bacteria are not readily disin- 

 tegrated and dissolved, there the phagocytes 

 of the blood and tissues come into play and, 

 through their power of engulfing these par- 

 ticles, operate as one of the body's main de- 

 fenses against infection. 



The unravelling of the intricacies of the 

 immune state, following upon the work of 

 Behring, has brought about a sudden and un- 



precedented enlargement of the scope of bac- 

 teriology, as well as supplied a wealth of new 

 facts of which many have permanently en- 

 riched practical medicine and opened new terri- 

 tory to profitable exploration.. It may suffice 

 at this point merely to mention certain of the 

 devices for diagnosis and means of preventing 

 or of treating disease, which are the immedi- 

 ate heritage of studies in the field of im- 

 munity, of which many have come not as di- 

 rect fruits, but as invaluable by-products of 

 the search. In this manner have been secured 

 the Widal test for typhoid fever, the Wasser- 

 mann and allied reactions, the hypersensitive 

 or Schick test for diphtheria susceptibility, the 

 hypersensitive reaction as now applied to the 

 detecting of the offending agency in hay fever 

 and allied states, the refinements of bacterial 

 vaccination in the prevention and sometimes 

 in the treatment of disease, and so-called spe- 

 cific serum therapy. Moreover, these studies 

 have placed in the hands of the bacteriologist 

 a powerful instrument for detecting, through 

 immunity reactions carried out in test tubes, 

 or the animal body, new varieties of patho- 

 genic or disease-producing bacteria and of in- 

 vestigating more closely and sorting out groups 

 of pathogenic microbes not hitherto subject to 

 analysis. Finally, the immunity reactions, as 

 they are generically named, have been found 

 not to be restricted to bacterial cells and poi- 

 sons, but to apply to a wide variety of cells 

 and their products. For it should be recalled 

 that in the decade immediately succeeding the 

 discovery of antitoxin, agglutinins, precipitins, 

 bacteriolysins, cytotoxins, hemolysins, com- 

 plements, chemotaxis, anaphylaxis, and the 

 minutiae of phagocytosis were discovered and 

 became the objects of animated and often fev- 

 erish and sometimes controversial but always 

 profitable investigation. 



It happened also and quite naturally and 

 logically that this should be the heyday of 

 hypotheses concerning the biological basis of 

 immunity and the manner in which interac- 

 tion takes place between toxin and antitoxin 

 inside as well as outside the body, and of the 

 englobing of bacteria and other bodies by the 

 blood and tissue cells, as well as the nature of 



