528 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



the production of immune substances presupposes the power of the tissues 

 to respond with primary reactions against the foreign material. The chemical 

 differentiation is not yet completed in fetal or newly-born organisms, as is 

 evidenced by their diminished power to act as antigens. Perhaps this lack 

 of available antigen in certain cells may be responsible for a diminution in 

 their binding power for toxic substances and in their ability to react against 

 the latter. Moreover, it seems that, as we have seen in the case of the blood- 

 group agglutinogens, differentials may develop in certain cells before the 

 mechanisms have developed which lead to the production in the serum of 

 specific substances interacting with those differentials. Such observations 

 permit the conclusion that in the embryo and fetus some substances, which 

 are present in the adult organism and which may function as antigen, are 

 lacking, and likewise, that the earlier ontogenetic states have not yet acquired 

 the full power to react against and to neutralize strange and toxic substances. 

 In agreement with this interpretation are certain experiments of Theobald 

 Smith and R. B. Little, who noted that newborn calves are prone to acquire a 

 generalized infection with colon bacilli; this can be prevented if the calves 

 are fed colostrum or receive the serum of a lactating cow. The deficiency in 

 globulin in the blood of newborn calves prevents the production of agglutinins 

 in these animals (Orcutt and Howe). P. Cannon suggests that the availa- 

 bility of globulin for the production of immune substances is the essential 

 factor on which depends the ability of an animal to respond with immune 

 processes to injurious interferences. Globulin is relatively deficient in very 

 young, and again in old individuals and also under unfavorable conditions of 

 nutrition. While this factor may play an important role in determining the 

 degree of resistance of an animal to an injurious condition, it is probably not 

 the only one which is active. 



But there exists, on the other hand, also some evidence which indicates that 

 the embryo and fetus, and even the organism at the time of birth, may pos- 

 sess substances which are able to act as antigens and which are not possessed 

 by the adult organism. Thus Lockemann and Thies, and Graefenberg and 

 Thies, found that it is possible to sensitize adult rabbits with the serum of 

 rabbit fetuses, and that a second injection of such serum causes anaphylactic 

 shock in the sensitized animals ; even the mother can thus be sensitized against 

 the blood serum of its own fetuses. It appears, furthermore, that during the 

 later stages of pregnancy, rabbits as well as guinea pigs become naturally 

 sensitized against a substance in the blood of their fetuses, the pregnant rabbit 

 and guinea pig being sensitive to the injection of the blood of newborn ani- 

 mals belonging to the same species. However, in addition to these effects, toxic 

 substances of another kind may apparently be active in pregnant animals ; it 

 has been stated that the latter are sensitive also to the injection of the blood 

 serum of pregnant animals belonging to the same or different species, while 

 normal guinea pigs seem to be more sensitive to the serum of puerperal than 

 to that of pregnant animals. 



We do not need to conclude, as have some investigators, that the earlier 

 ontogenetic stages represent different and phylogenetically more primitive 



