30 IMMUNO-CATALYSIS 



during the first 1 5 seconds 1 g. of enzyme is responsible for the produc- 

 tion of 825 g. of CO2, at a rate of 1 .24 moles CO2 per sec. per g. of 

 enzyme (Roughton, 1934); urease crystals possess an activity of a 

 little more than 100,000 units per gram, or 100,000 mg. of ammonia 

 nitrogen is produced in five minutes when acting on urea at 20°C. at 

 pH 7.0 (Sumner, 1932); solutions made of crystalline trypsin or pepsin 

 containing less than 1/1,000,000 (0.000,005 M) of a gram of protein 

 nitrogen per ml. have an accurately measurable effect on the digestion 

 of casein, while solutions of pepsin containing less than 1/10,000,000 

 of a gram of protein nitrogen have a very powerful effect on the 

 clotting of milk (Northrop, 1932). One g. of crystalline pepsin 

 dissolves 50,000 g. of boiled egg white in two hours, clots 100,000 

 liters of milk and liquefies 2000 liters of gelatin during the same 

 period of time. One g. of purified rennin (Tauber and Kleiner) 

 clots 4,500,000 g. of milk in ten minutes. 



c. Disproportionality between the Amount of the Antigen Used 

 and the Amount of Antibody Produced. The measurement of the 

 amount of antibody produced in response to a given amount of anti- 

 genic substance encounters considerable technical difficulties, some of 

 which are almost insurmountable. These difficulties are: (1) although 

 the circulating antibodies could be approximately estimated by pre- 

 cipitin and agglutination reactions, we have as yet no way of determin- 

 ing the amount of the antibody fixed in the tissues; (2) we cannot 

 determine the actual amount of antigen responsible for the antibody 

 produced; it is not unlikely that only a fraction of the injected substance 

 is instrumental in the production of antibody; (3) when whole organ- 

 ises are used we have no idea of the number of antigenic molecules 

 in an injected quantity of bacteria. Despite these difficulties the prev- 

 alent opinion among immunologists and bacteriologists is that there 

 is a striking disproportion between the quantity of antigen and the 

 total amount of the resulting antibodies. 



As early as 1893 it was demonstrated (Roux and Vaillard, 1893) 

 that continuous bleeding of horses actively immunized against tetanus 

 toxin did not diminish the antitoxin content of the regenerated blood. 

 In similar studies (Salomonsen and Madsen, 1898) on diphtheriae 

 toxin used to immunize horses, the above observation was confirmed. 

 Much more interesting was the observation that when the antibody 

 diminished, or nearly completely disappeared, the administration of 



