MECHANISM OF ANTIBODY FORMATION 57 



synthesis occurs under the specific stimulus of an antigen. No excep- 

 tion to this rule has as yet been found. The presence of C^^ in the 

 assayed antigen-antibody precipitates could, perhaps, be best explained 

 in the following manner: (a) Antibody globulin molecule can ex- 

 change amino acid residues in a dynamic environment without under- 

 going appreciable digestion or losing parts from the basic antibody 

 molecular unit; (b) normal serum components and the minimum 

 antibody molecular units (e.g., diphtheria antitoxin, etc.) can enter 

 into reversible combinations, as shown below: 



Normal serum component + antibody unit ^ Antibody Complex 

 (containing C^"*) 



and (c) the extreme precaution taken to remove possible C^* irnpuri- 

 ties from the antigen-antibody precipitates was perhaps inadequate and 

 drastic dialysis at various [H + ] might have been necessary to remove 

 the C^'* impurities from the reactants to start with. 



With this in mind, the following observations concerning the length 

 of time an antigenic substance can reside in a host are presented. 

 According to Uhlenhuth and Weidanz (1909) 5 ml. of horse serum in- 

 jected intravenously into a rabbit was found in the blood 1 5 days after 

 the injection. With the gradual increase of precipitin there was a cor- 

 responding diminution of the horse serum. Longcope and Mackenzie 

 (1920) reported that 5 ml. of horse serum per kilo body weight of 

 rabbit injected intravenously was detectable after three weeks. These 

 latter investigators studied also the presence of horse serum at given 

 intervals after its injection into human beings for therapy of pneu- 

 monia. The results of experiments with 14 individuals, who received 

 from 100 to 500 ml. of antipneumococcal horse serum intravenously 

 yielded results falling into two groups. 



In the first group of eight cases, the persistence of horse serum 

 ranged from 18 to 39 days. The injection of horse serum was followed 

 by severe serum disease, lasting from 11 to 28 days, and as a rule the 

 precipitins appeared first or their concentration increased markedly 

 towards the end of the serum disease. On the other hand, the pre- 

 cipitin reaction for horse serum diminished rapidly towards the termina- 

 tion of the serum disease and disappeared shortly thereafter. In the 

 second group of 5 cases, the precipitinogen in the serum persisted from 

 49 to 69 days. The precipitin formation was either of extremely short 



