644 THE INTERNAL SECRETIONS AND IMMUNITY. 



a long period subsequently, and the endurance of the horse 

 remained unchanged for months, but the antitoxicity of its 

 blood gradually declined, until from 1400 units it fell to 100 

 units. 



"This rather sudden appearance of the antitoxin and its 

 decline during the immunity of the animal prepare us for the 

 information that the animal's immunity does not depend upon 

 the antitoxin, but upon some other condition. The probable 

 proof of this is seen in the peculiar condition of hypersensitivity 

 to which Behring and Wladimiroff called attention, and of 

 which mention has been made. In these cases it makes no 

 matter how much antitoxic strength is contained in the blood, 

 the animal is just as sensitive to the toxin as if it had none, 

 and as if it had not been immunized. Moreover, the hyper- 

 sensitivity is not a cumulative action of the toxin that out- 

 weighs the antitoxin, as will be readily shown by a simple 

 calculation. A horse weighing 1300 pounds, possessing about 

 100 pounds of blood, of which about one-third, or 30 pounds, 

 is serum, has been immunized to diphtheria toxin according 

 to the method described in the chapter upon 'Diphtheria'; 

 and while the serum contains 500 immunizing units of anti- 

 toxin in each cubic centimeter of blood-serum, the horse falls 

 into the hypersensitive condition and dies. What relation 

 exists between the antitoxin in its blood and the toxin that 

 produced death? 



"It is certain that there is none, and that the antitoxin 

 that exerts a most remarkable protective influence upon other 

 animals does not protect the animal by which it is formed. 



"If the horse's blood furnishes a total of 30 pounds of 

 serum, each pound being about equal to 500 cubic centimeters 

 of liquid, there is a total of 15,000 cubic centimeters of anti- 

 toxic serum in the horse. 



"Suppose the minimum fatal dose of diphtheria toxin for 

 a 250-gramme guinea-pig to be 0.0045. If the serum under 

 consideration contain 500 units in each cubic centimeter, then 

 Vsoooo cubic centimeter will protect a guinea-pig against 0.0045 

 cubic centimeter of the toxin; VBOOO cubic centimeter against 

 0.045 cubic centimeter; 1 / BOO cubic centimeter against 0.45 

 cubic centimeter; Y 50 cubic centimeter against 4.5 cubic 



