223 



perimenlal and control c'lilliircs wci-c used as tests lor 

 measuring the resistance gained Ijv tlie immunized (issue 

 at a given time din'ing the experiment. The test was car- 

 ried oul in such a way that the remaining halves of the 

 experimental and control cultures were placed in a culture 

 medium containing the antigen in a high concentration. 

 50 — 06 per cent, which was Found to have :i marked in- 

 hibiting action on the growth of normal tissues. If the 

 tissue grown in a medium containing a small amount of 

 antigen did not constantly become immunized, its rate of 

 growth would be as low as that of the control tissue, 

 when both were ex])osed to a high concentration of the 

 antigen. Therefore, the (juotient of the rate of growth 

 of the experimental subculture (immunized strain 

 in the high concentration of antigen) divided by the rate 

 of g r o w t h o f t h e control subculture (non-immuni- 

 zed strain in the high concentration of antigen) expressed 

 the degree of resistance or immunization. If both immunized 

 and non-immunized strains, for instance, grew at the same 

 rate in a high concentration of the toxic antigen, the quotient 

 would be 1, and no immunization had taken place. If the 

 immunized strain grew more actively than the non-im- 

 munized strain, the quotient would be higher than 1. and 

 express the degree of resistance. 



It was observed that the j'ate of growth of the two 

 strains during 19 passages (about 10 days) was practically 

 uniform, table 21 and fig. 46. The fluctuations of the rale 

 of growth are due, to some extent to the slight changes in 

 temperature of the incubatoi' and similar periodical causes. 

 In the beginning when the control showed a high rate of 

 growth, the experiment showed a lower rate, and vice 

 versa, but after about 8—10 passages both cultures showed 

 fluctuations in the same direction. 



Subcultures were made of the control (non-immunized 

 strain) and both transferred into a medium composed of 

 plasma, embryonic tissue juice, and the antigen. In one 



