126 PATHOGENIC BACTERIA. 



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 c.c. of 

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

 antitoxic serum in the horse. 



Suppose the minimum fatal dose of diphtheria toxin 

 for a 250-gram guinea pig to be 0.0045. If the serum 

 under consideration contain 500 units in each cubic cen- 

 timeter (see the method of testing diphtheria antitoxic 

 serum in the chapter upon Diphtheria), then ?0 ^ 00 c.c. 

 will protect a guinea pig against 0.0045 c - c - °f the toxin ; 

 g^oir c.c. against 0.045 c - c -5 5-00 c - c - against 0.45 c.c; 

 ^q- c.c. against 4. 5 c.c. ; \ c.c. against 45 c.c. ; and 1 c.c. 

 against 9 c.c. of the toxin. If each cubic centimeter of 

 the serum of this horse is capable of destroying the toxic 

 effect of 9 cubic centimeters of toxin, the total toxin- 

 annulling capacity is 9x15,000 c.c. of serum in the 

 horse's blood = 135,000 c.c. of toxin. 



We must next see how much toxin has been received 

 by the horse during his immunization. The follow- 

 ing doses, the figures referring to cubic centimeters of 

 toxin, probably represent an average careful manipu- 

 lation extending over a period of about three months : 

 -nr, h h *> ** 2, 3, 5, 8, 10, 15, 20, 25, 50, 50, 100, 150, 

 200, 250, 300, 500, 500, 500, 500, making a total of about 

 4200 c.c. of diphtheria toxin. Now observe that the 

 total quantity of toxin consumed by the horse is 4200 c. c. , 

 but his protective energy is 135,000 c.c. of toxin, so that 

 the blood of this horse, if drawn from his body, would 

 furnish enough protection to save 327- horses from doses 

 of toxin as large as the total amount administered to 

 him during the entire course of his treatment. 



This illustration is not only extremely instructive in 

 showing the paradoxic nature of the condition of hyper- 

 sensitivity, but certainly proves that the antitoxicity of 

 the blood is not the cause of immunity, but a phenome- 



