244 PASSIVE IMMUNIZATION 



TETANUS. 



The preparation and titration of tetanus antitoxin is based upon 

 practically the same principles as that of diphtheria antitoxin, which 

 we have considered in some detail in the foregoing section. The 

 standards employed in Germany are the following: 



One unit of toxin is that quantity which is capable of killing 

 4,000,000 white mice (of an average weight of 10 grams each) within 

 four or five days with the characteristic symptoms of tetanus. 



A toxin solution of such strength that 1 c.c. contains one unit of 

 toxin is designated as normal toxin. 



One unit of antitoxin is that quantity which will protect a mouse 

 weighing 10 grams against 4,000,000 fatal doses of toxin, when 

 injected subcutaneously. 



A normal antitoxic serum is one of which 1 c.c. contains one unit 

 of antitoxin. 



In the United States an official standard unfortunately does not 

 yet exist, and as the standards of the different manufacturers are 

 not alike, physicians are practically obliged to express their dosage 

 in terms of cubic centimeters rather than in antitoxin units. 



Von Behring's fluid antitoxin is marketed in 100-unit (10 c.c.) 

 and 20-unit (2 c.c.) doses; in addition to this a solid antitoxin, of 

 which 20 units represent a dose, is also available. 



Dosage and Uses. For prophylactic purposes, 20 units (2 c.c.) 

 should be injected about the site of injury, and if large nerve trunks 

 have been exposed, in part into their substance: the idea being to 

 bind the toxin which is formed about the point of infection, before 

 it leaves this district, which takes place along the lymphatics and 

 the nerve fibers. At the same time, it is recommended to give a 

 subcutaneous injection of 100 additional units (10 c.c.) at an indiffer- 

 ent point, and to repeat the dose within six to eight weeks, as the 

 immunity which is afforded only lasts for that length of time. 



When symptoms of tetanus already exist, the idea has been that 

 very little is to be expected from the use of the antitoxin for the 

 reason that these symptoms indicate that a union with sensitive 

 receptors (in the central nervous system) has already occurred, 

 and that the antitoxin cannot penetrate to those points from intact 

 bloodvessels. For this reason neither the subcutaneous nor the 

 intravenous route offers much hope of a satisfactory result. The 



