518 INFECTION AND RESISTANCE 



and have become accustomed to the test tube conditions they entirely 

 lose their virulence, are easily attacked by the active constituents of 

 animal serum, and are probably amenable to phagocytosis. When 

 such cultures, living or dead, are injected into animals they act like 

 other specific protein antigens and incite the formation of antibodies. 

 However, these antibodies have no effect whatever upon the virulent 

 organisms. 



In consequence, it cannot astonish us that all efforts at passive 

 immunization with the sera of syphilitic man and animals, or with 

 those of animals systematically treated with dead virulent materials, 

 have been unqualified failures. 



However, this does not preclude the theoretical possibility of 

 active immunization or vaccination with such materials since, in this 

 case, the antigen distributed from the points of injection might act 

 upon tissue cells throughout the body. However, with the exception 

 of the unconfirmed reports of Spitzer, all attempts to vaccinate 

 either with dead virulent material, or with living and dead culture 

 material, have been disappointing. The few experiments of Metch- 

 nikoff with virus "attenuated" by passage through monkeys have 

 indeed seemed to indicate some possibility of approaching the subject 

 from this direction, but these isolated observations have been very 

 logically criticized by Neisser and should not bear too much weight. 

 The observations were made on two cases only, both of them well 

 along in life, and the validity of the important conclusions drawn 

 rests entirely on the always problematical fulcrum of complete ex- 

 clusion of previous syphilitic infection in the two subjects. More- 

 over, attempts in this direction would be fraught with a considerable 

 amount of danger and it is therefore questionable whether experi- 

 mentation along these lines is sufficiently promising to be justified. 

 There is certainly no attenuation for man by passage through rabbits 

 as has been sufficiently proven by a number of accidental infections, 

 an instance of which in a laboratory attendant has been reported by 

 Graetz and Delbanco. 176 



We may state, therefore, as safely summarizing our knowledge 

 of the conditions in syphilis, that the resistance which undoubtedly 

 develops during the course of the disease is one which depends upon 

 reaction to the living virus only, cannot so far be produced in animals 

 by systemic treatment with dead treponemata, and does not express 

 itself in the formation of significant amounts of circulating anti- 

 bodies analogous to those observed in bacterial diseases. Moreover, 

 it is a well-known fact that the treponemata can continue to do injury 

 to many organs and tissues at a time when reinfection by the paths 

 of skin and mucous membranes is no longer possible. 



How, then, are we to explain this peculiar state of affairs? A 

 clue to the problem we think is found in the 20 rabbits which Hop- 



176 Graetz and Delbanco. Med. klin., 1914, 375 and 420. 



