650 



SCIENCE 



[N. S. Vol. XXVII. No. 695 



Such relapses are practically absent with 

 the Moscow strain, very slight with that of 

 the New York and more common with the 

 African strains. 



In the case of S. Duttoni the "cure" is 

 not always as marked as with the other 

 three, depending as it does, first, upon the 

 dose and efficiency of the serum employed, 

 and, second, upon the stage of infection. 

 The latter is a most important factor. 

 Eats in the early stage of infection with 

 this organism (that is, on the first day fol- 

 lowing the injection of spirilla) are readily 

 cured within half an hour without any 

 untoward eflleet. The administration of 

 the serum on the second day of the disease, 

 at a time when the blood is swarming with 

 spirilla, leads to agglutination and solution 

 of such masses of organisms that death 

 from intoxication and obstruction is the 

 usual result. "When the animal survives, 

 the spirilla may continue to persist in some- 

 what lessened numbers. This latter fact is 

 due to the presence of "immunized" or 

 "serum-fast" spirilla. Hence, in the treat- 

 ment of this disease it is not advisable to 

 employ a curative serum, in large doses, at 

 the time of maximum infection. 



The S. Duttoni is especially prone to 

 reciprocal immunization, since this organ- 

 ism can be found at times in large num- 

 bers, in the blood of hyperimmunized ani- 

 mals. This serum-fast property, first dem- 

 onstrated for S. Kochi by Levaditi and 

 Roche, is especially marked with *Si. Dut- 

 toni, and the recognition of this state offers 

 a most rational explanation of the cause 

 of ordinary relapse as well as that follow- 

 ing the curative treatment. Hitherto it 

 was believed that the relapse was due to 

 the survival, in extravascular spaces, of 

 spirochetes which after the partial destruc- 

 tion or elimination of the specific anti- 

 bodies were able again to invade the circu- 

 lation. In the light of the facts now 

 known it is clear that the relapse is due 



to the survival of a few individuals which 

 have acquired more or less immunity to 

 the specific germicidal bodies elaborated in 

 the infected animal. As a result a new 

 "serum-fast" strain develops, which in 

 turn calls for a new anti-body. The latter 

 is apparently not as active as the first, or 

 is more unstable, or is more readily elim- 

 inated, and hence the continuance of the 

 relapses with this organism. This adapta- 

 tion of spirilla would appear to be least 

 marked with the Moscow spirillum, since 

 with it relapses in rats are scarcely recog- 

 nizable. On the other hand, S. Duttoni is 

 at the other extreme, and from what is 

 known of the mortality in the Bombay 

 fever, it may be inferred that the S. Car- 

 teri will be found to be even more prone 

 to relapse in rats. 



As pointed out by Levaditi, the serum- 

 fast character is perhaps a fixed property 

 of S. pallidum, and without doubt this con- 

 ception accoimts for the persistence of that 

 organism within man better than any other 

 theory. The difficulty of producing a 

 curative serum for the syphilitic spirochete 

 will be readily seen. The phenomenon of 

 reciprocal immunization is not limited to 

 this group, for, indeed, it was first recog- 

 nized in the study of trypanosomes. 

 Neither can it be adduced as a character- 

 istic of protozoa, for like conditions are 

 now known to exist with various bacteria, 

 and this fact must, therefore, be taken into 

 consideration in the treatment of bacterial 

 disease with anti-sera. Many data are now 

 at hand which go to show the existence of 

 a plurality of strains for nearly every 

 pathogenic organism. And, moreover, such 

 modifications must be expected if we as- 

 sume, as there is good reason to, the exist- 

 ence of labile groups in the living molecule. 



The practical application of the curative 

 action of a given immune serum, it will be 

 seen, is restricted to the infection caused 

 by the corresponding spirochete, and hence 



