MECHANISM OF ANTIBODY FORMATION 55 



linked at the terminal part of the chain to one molecule of p-amino- 

 benzoic acid through a carboxyl group, as reported by Ratner, et at. 

 (1944). It is also to be noted that gramicidin and tyrothricin obtained 

 from B. hrevis are polypeptide containing natural 1- and unnatural 

 d-amino acids. These polypeptides are resistant to the action of crude 

 trypsin, pepsin, papain and papaya latex at several pH values (Hotch- 

 kiss, 1944). This resistance is attributed to the d-amino acid contents 

 of these polypeptides which exercise antibacterial action and toxicity 

 for animal cells and tissues. 



The consideration of the above cited observations may help us to 

 visualize the structural differences of antigenic substances derived 

 from animal, plant and bacterial sources. These differences, no doubt, 

 play a significant role in resisting the host enzymes and thereby pro- 

 longing the life of antigenic substances and the immune response they 

 produce in a host. In this connection, the following observations are of 

 interest. In a study on the behavior of antibody protein toward dietary 

 nitrogen in active and passive immunization, the following experiment 

 has been carried out (Heidelberger, et al; Schoenheimer, et al. 1942). 

 A rabbit actively immunized against Type III pneumococcus was given 

 a single large injection of Type I antipneumococcal rabbit serum. The 

 administration of isotopic glycine by addition to the stock diet was 

 started two hours before injection and continued for 48 hours. Daily 

 estimations of the amount of circulating antibody (passively admin- 

 istered) and of the isotopic N^^ concentration of antibody and residual 

 proteins were made. Since, in this passive immunization, the antibody 

 introduced could only be hydrolyzed but not be regenerated, its daily 

 estimation gave an idea as to how long it could persist in the rabbit act- 

 ing as a species specific host. At hour the amount of passively intro- 

 duced Type I antibody corresponded to 1 .09 mg. of total antibody nitro- 

 gen/ml. of serum. After 22V^ hours it was 0.88 and after 48 hours 0.49 

 mg. of total antibody nitrogen/ml. of serum. Thus 55 per cent of the 

 passively introduced antibody was eliminated within 48 hours. Atten- 

 tion was drawn to the fact that the passively introduced antibody 

 enters into metabolic reactions which lead to its disappearance, but 

 not to the regenerative uptake of nitrogen, as in the case of actively 

 produced antibody. The failure of passively introduced antibody to 

 take up heavy nitrogen, they stated, can less reasonably be ascribed to 

 a generalized "foreign protein" character than to the absence of some 



