542 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



so similar that they cannot give origin to organ-specific immune substances. 

 On the other hand, certain water soluble, heat sensitive substances, pre- 

 sumably of protein nature, in brain and epiphysis represent organ differ- 

 entials which do permit the distinction between these two organs. However, 

 while these two kinds of immune sera react most strongly with the 

 homologous organ extract, a weaker reaction takes place also with the other 

 organ suspension. This is probably due at least partly to the presence of 

 common organismal (species) differentials in brain and epiphysis, as is 

 indicated likewise by the fact that the immune sera against unheated beef 

 brain and epiphysis suspensions react also with beef serum. 



7. Fleisher showed that in liver and kidney there exist species- specific as 

 well as organ-specific substances ; in addition to strictly organ-specific sub- 

 stances there are others which are similar to or identical with substances 

 present in certain other organs. He used the complement fixation test, but 

 before making the latter he determined the presence of specific and other not 

 strictly specific substances in the immune sera by means of absorption. 

 Also, according to Witebsky, immunization with suspensions of kidney and 

 liver leads as a rule to the production of both species- and organ-specific 

 antibodies, but the former predominate. It is also of interest that precipitins 

 and hemolysins do not develop as readily after injection of these organ 

 suspensions as after injections of serum proteins and erythrocytes; they are 

 found only in some of the immune sera against these suspensions. 



In recent experiments Henle and Chambers showed that if rabbits are 

 immunized with particles 0.1-0.3 micra in diameter, obtained through centrif- 

 ugation of various organ suspensions of the mouse, organ-specific agglu- 

 tinins can be obtained from brain, liver, kidney and testicle ; negative or 

 doubtful results were obtained from muscle, lung, pancreas and spleen. Liver 

 and brain particles from ferret reacted likewise in an organ-specific manner 

 with the corresponding anti-mouse sera, whereas ferret kidney and muscle 

 particles behaved differently. These experiments indicate therefore a very 

 marked organ-specificity of several organs of the mouse, which may have 

 been associated with a species specificity. These particles consisted of nucleo- 

 proteins as well as other extractable substances (lipids). Claude had formerly 

 shown that similar particles behave tinctorially and chemically like mito- 

 chondria. It is therefore possible that in these experiments mitochondria 

 were the substratum which yielded the organ-specific reaction, but it is more 

 probable that these particles corresponded to the "particulates" which Bensley 

 described in the liver of guinea pigs; these particulates are similar in their 

 chemical constitution to mitochondria, but they are smaller in size. 



8. In this connection we may also refer again to the experiments of Mann 

 and Welker, who found that it is possible to produce in rabbits precipitins 

 for the proteins of human and rat carcinoma. The immune sera against 

 human cancer reacted with autolysates of human cancer, but not with those 

 of rat cancer, and the immune sera against rat cancer reacted with autolysates 

 of rat cancer, but not with those of human cancer. There was some indica- 

 tion that the number of positive results was greater if the cancerous tissue, 



