REACTIONS OF NEWBORN AND ADULT ORGANISMS 525 



chicken serum, the blood of young chickens did not contain an active antigen 

 which, when mixed with the precipitin of the immune serum, induced forma- 

 tion of a precipitate. Kritschewski noted that a substance obtained from nine- 

 week-old tadpoles of Rana esculenta can be differentiated in its antigenic 

 function from the substance of adult frogs by means of the complement fixa- 

 tion test, and he likewise observed that the Forssman antigen, which is present 

 in the erythrocytes and organs of adult chickens, is not yet present in the tgg 

 and in very young embryos, but that it forms four days after the beginning of 

 segmentation, when a more advanced embryonal stage has been reached. 



These experiments, indicating that antigens develop only gradually during 

 embryonal life, agree with the findings mentioned previously concerning the 

 blood-group differentials, which seem to begin to form prior to the sixth 

 month of pregnancy, but reach their full development only at about the time 

 of puberty. It is necessary to select an especially active isoagglutinin in order 

 to effect the agglutination of young as compared with older blood corpuscles. 

 Likewise, the two different varieties of the A differential, A and A 1 (Thorn- 

 sen), or A x and A 2 (Landsteiner), which differ in their binding power for 

 isoagglutinin, gain their full strength only gradually with advancing childhood. 

 While thus, in the course of time, the' blood corpuscles acquire properties 

 which enable them to bind a greater quantity of isoagglutinin, the difference 

 in the ability of the A and A x corpuscles to combine with isoagglutinin re- 

 mains preserved also at later periods. 



Similarly, according to Thomsen, the full development of the isoagglutinin 

 occurs only sometime between the fifth and tenth year of life, while in old 

 age it may decrease again (Schiff and Mendlovitsch). Also, the natural 

 amboceptor and complement of hemolysin, as well as the corresponding sub- 

 stances acting with bacterial substances, are not yet present in the earliest 

 embryos, but form as embryonal life progresses in chicken and cattle (Sachs, 

 Rywosch). In the chicken embryo, antibodies first appear after the twenty- 

 first day. In very young swine embryos only very small amounts of comple- 

 ment, hemolysin-amboceptor and opsonin are found ; these increase during 

 embryonal development (Sherman). In this connection we may also cite the 

 observation that while in the Freund-Kaminer test normal adult human sera 

 are able to dissolve cancer cells, the sera of human fetuses do not yet possess 

 this ability, and resemble in this respect the sera of persons afflicted with 

 cancer. 



It is well known that different species of animals differ very much in their 

 power of resistance to certain bacteria and toxins. Similarly, the reactivity of 

 young organisms to various toxins and bacteria may differ from that shown 

 by adult organisms. Thus, according to Camus and Gley, the erythrocytes of 

 newly-born rabbits are more resistant to eel serum than those of older in- 

 dividuals. Newly-born chicks and rabbits are not sensitive to arachnolysins 

 and are less sensitive to cobra toxin. Heterohemolysins may be found in 

 smaller quantity in younger than in older individuals, the amount of ambocep- 

 tor as well as of complement being less in younger organisms. These observa- 

 tions agree with the findings in other experiments of Sachs, in which he 



