CAN ORGANISMAL DIFFERENTIALS BE CHANGED? 587 



may have, perhaps, to deal here with a coating of the outer ectoplasmic layer 

 of the bacteria with the serum, which would confer on this layer the character- 

 istics of the foreign serum. 



Also, observations of Thomsen, Friedenreich and Hallauer, may have some 

 bearing on this problem. Thomsen (1927) showed that it is possible to 

 change human erythrocytes, irrespective of the group to which they belong, 

 in such a way that they can be agglutinated by human serum, even if the 

 latter does not have a definite relation to the blood group of the red corpuscles 

 used. This change can be affected by exposing the erythrocytes to contact 

 with certain bacterial cultures or their filtrates. Thomsen and Friedenreich 

 explained this effect by assuming that under these experimental conditions a 

 new specific receptor "T" is produced in the erythrocytes. In the normal sera 

 of certain dogs, sheep, hogs, rabbits, guinea pigs, and also of certain mice, 

 there may be found a T agglutinin acting specifically on the experimentally 

 produced agglutinable substance. The T agglutinin is distinct from the normal 

 group-specific agglutinins, anti-A and anti-B. Hallauer, with the aid of 

 immune agglutinins specific for this agglutinable substance, was able to prove 

 that a T receptor had actually been newly formed in red corpuscles of man, 

 as well as of certain other animal species, which had been exposed to such 

 bacterial filtrates. The corresponding immune agglutinins could be absorbed 

 by such erythrocytes, and there is, moreover, some indication that the species 

 differential of these corpuscles is also concerned in the production of these 

 immune bodies, the antigen, presumably representing a combination of a 

 special agglutinable factor and an organismal differential, acting as carrier. 

 As usual, the carrier must be of a heterogenous nature, in respect to the species 

 which is being immunized. In this case, therefore, there would have been experi- 

 mentally effected a change of a character which, while determined by nuclear 

 genes, affects a cell no longer possessing a nucleus. This result cannot depend 

 upon a somatic mutation of a gene, but it must be due to the alteration of a 

 factor localized in the cytoplasm. Inasmuch as red blood corpuscles do not 

 multiply, the acquired characteristic in this instance is not transmitted to 

 successive generations of cells ; however, it is quite conceivable that a cyto- 

 plasmic change, acquired by cells which have the power to propagate, might 

 be transmitted to many successive cell generations. 



The mechanisms, to which may be attributed these experimental changes 

 produced in single cells and in tumor tissue, are not yet understood, and the 

 findings here reported do not contradict the concept that organismal differ- 

 entials in higher organisms depend on the genetic constitution of the individ- 

 ual and find expression by means of reactions which presumably take place 

 in cytoplasmic structures. Alterations in these manifestations are therefore 

 not necessarily caused by changes in genetic factors as such, but by modifica- 

 tions which environmental conditions produce in cells and tissues. 



On the other hand, it cannot be excluded at present that certain persistent 

 modifications produced in parasitic or also in free-living protozoa may be due 

 to genetic changes caused by adaptative alterations which were induced by 

 environmental conditions. The fact that they are liable to be lost particularly 



