228 BACTERIA PATHOGENIC TO MAN 



of antitoxin to neutralize it. In five days this dose is doubled, and 

 then every five to seven days larger amounts are given. After the 

 third injection the antitoxin is omitted. The dose is increased as 

 rapidly as the horses can stand it, until they support 700 to 800 c.c. or 

 more at a time. This amount should not be injected in a single place, 

 or severe local and perhaps fatal local tetanus may develop. After some 

 months of this treatment the blood of the horse contains the antitoxin 

 in sufficient amount for therapeutic use. When the animals' tempera- 

 tures are normal and they have recovered from the dose of toxin last 

 given, they are bled into sterile flasks and the serum collected. A quicker 

 and safer method of immunization is to mix antitoxin with larger doses 

 of toxin in the first four injections. 



Technique of Testing Antitoxin Serum for Value in Antitoxin. Tetanus 

 antitoxin is tested exactly in the same manner as diphtheria antitoxin,, 

 except that the unit adopted by different dispensers is different. This 

 confuses the physician and almost compels him to give a certain number 

 of cubic centimetres without regard to the units contained. The amount 

 of antitoxic serum which neutralizes an amount of test toxin which 

 would destroy 40,000,000 grams of mouse contains 1 unit of antitoxin 

 by the German standard. One large American producer considers 

 1 unit of antitoxin to be the amount which neutralizes only 100 grams 

 of mouse. In the French method the amount of antitoxin which is 

 required to protect a mouse from a dose of toxin sufficient to kill in 

 four days is determined, and the strength of the antitoxin is stated 

 by determining the amount of serum required to protect 1 gram of 

 animal. If 0.001 c.c. protected a 10-gram mouse the strength of that 

 serum would be 1 : 10,000. Guinea-pigs are sometimes used in place 

 of mice. The United States government should make an official tetanus 

 antitoxin unit in the same way it has an official diphtheria antitoxin 

 unit. The toxin used for testing is preserved by precipitating it with 

 saturated ammonium sulphate and drying and preserving the pre- 

 cipitate in sealed tubes. As required, it is dissolved in 10 per cent, 

 salt solution as above stated. For small testing stations the best way is 

 to obtain some freshly standardized antitoxin and compare serums 

 with this. 



Persistence of Antitoxin in the Blood. Ransom has recently shown 

 that the tetanus antitoxin, whether directly injected or whether produced 

 in the body, is eliminated equally rapidly from the blood of an animal 

 provided that the serum was from an animal of the same species. If 

 from a different species it is much more quickly eliminated. From 

 this we see a possible explanation of the fact that immunity in man, 

 due to an injection of the antitoxic serum of the horse, is less per- 

 sistent than immunity conferred by an attack of the disease. 



The same author found some interesting facts in testing the antitoxic 

 values of the serum of an immunized mare, of its foal, and of the milk. 

 The foal's serum was one-third the strength of the mare's, and one 

 hundred and fifty times that of the mare's milk. In two months the 

 mare's serum lost two-thirds in antitoxic strength, the foal's five-sixths, 



