232 



tween the amoiinl of antigen, the time of \hv :i|)|)('ar;iiice( 

 of the imnuinization and its diiratioii. 



^^hclluM• the ])lu'ii()inen()n dcscrilji'd here really is an im- 

 mune proeess inasmuch as llic ril)r()l)lasls aetually produce 

 anlil)()dies. is of course not yel proved by Ihese experiments. 

 To settle the question it is necessary to demonstrate the. 

 presence of antibodies in the cnllurc medinm of the im- 

 munized strain. If the culture medium of a non-immu- 

 nized strain is able to |)i-()tect the latter from the toxic 

 action of the antigen (passive immunization; it is proved 



12 3 4 5 6 7 8 

 Passage 



Fig. 52. 

 Curve stiowing the variations in ftie degree of immunization of fibroblasts 

 in vitro ttirougti eigtit passages. Dog serum was used as antigen in a con- 

 centration of 8 per cent. Ttie ordinates represent ttie quotient of tlie rate of 

 growtli of tlie immunized strain divided by ttie rate of growtti of ttie non- 

 immunized strain in a tiigti concentration of antigen, and ttie abscissae 

 ttie number of passages. 



tlial the acquired resistance is an actual process of immu- 

 nization. This has not j^et been done. 



If there is a veritable immune process going on here, 

 and not a simple adaption, which I do not believe, we have 

 then a simple technique for making fundamental studies 

 in this field of investigation and in clean-cut experiments 

 much simpler than if we work with the comi)lex organism. 

 At the same time, as the tissue cells produce antibodies 

 in vitro, we have in t h e r ate of g r o \\' I h of t h e s a m c 

 tissue an indicator for the degree of i m m u- 



