231 



of fibroblasts. l)o<^ sera wtM'o used whicb liad a inai'kcd 

 loxic effect on tbe fil)roi)Iasts. \\ ben 1.1 jxt cent antij^en 

 was added lo the culture medium as a small daily dose, tbe 

 maxiuium degree of immunization or resistance was reached 

 at al)Out tbe 6—8 passage, (table 22 and fig. 51 . \Mu'n I 

 l)er cent antigen was added to Ihe culture medium, tlie 

 maximum degree of resistance was reached at tne 5th 

 passage, (table 23). When 8 per cent antigen was used, the 

 maximum degree of immunization was reached at the se- 

 cond passage already, (fig. 52, table 24,. A high concentra- 

 tion of antigen caused a quick rise of resistance wliicb 



o 

 Pi 





4 5 6 

 Passage 



6 



Fig. 51. 

 Curve showing ttie variations in tlie degree of immunization of fibroblasts 

 throughi nine passages. Dog serum was used as antigen in a concentration 

 of 1.4 per cent. Ttie ordinates represent tlie quotient of ttie rate of growtti of 

 ttie immunized strain divided by ttie rate of growtti of the non-immunized strain 

 in a high concentration of antigen, and the abscissae the number of passages. 



lasted only a short lime, whereas the maximum degree of 

 immunization was reached relatively late and lasted long, 

 when a small amount of antigen was used. This is also 

 found by earlier experiments in vivo, (T h o r b o r g ^■"^). 



The experiments here ai*e of course only to be con- 

 sidered as a kind of exploration in this field of investigation. 

 The results anyway show clearly that fibroblasts respond 

 also to the presence of a foreign protein in the medium and 

 become immunized and tliere is doubtlesslv a rehition be- 



