ANTI-TOXINS 73 



immunized horse received. Thus there is evidently a tremendous 

 overproduction of anti-toxin far above the needs of the animal. 



The various component parts of the toxin stimulate the cells of 

 the horse to produce the receptors, or anti-toxin. The toxoids, 

 themselves not poisonous, have the property of stimulating the 

 production of anti-toxin. We measure the anti-toxic powers of 

 the anti- toxin with units arbitrarily devised. An anti-toxic unit 

 is that amount of horse serum just necessary to protect a 2$o-gram 

 guinea pig against 100 times the minimum lethal dose of toxin. 



To standardize anti- toxin, we must employ animals, into the 

 bodies of which toxins and anti-toxins are injected. If a certain 

 amount of anti-toxin is necessary to protect a guinea pig against 

 ten times the minimum fatal dose of toxin per 100 grams of guinea- 

 pig weight, then we know that the anti-toxin contains so many 

 units. The minimum lethal dose of toxin is the smallest quantity 

 that will kill a guinea pig of 250 grams in four days. 



A standard anti-toxin is kept by governments to be used as a 

 control of the products of biological chemists. 



Against this standard anti-toxin a toxin of unknown strength is 

 measured by means of guinea pigs. The toxin unit thus found is 

 then used to determine the anti-toxic unit of anti-toxins of un- 

 known power. 



Anti- toxic serum is preserved by the addition of .5 percent of 

 tri-cresol or phenol. It remains practically unchanged in strength 

 for a year or more. 



It is not only of value as a curative agent, neutralizing the toxins 

 already formed, but is valuable as an immunizing one against in- 

 fection. Persons exposed to diphtheria and giving a positive 

 Schick test should be given an immunizing dose of 1,000 to 1,500 

 units. If injected early in a case of diphtheria, it is much more 

 likely to do good, than if used later. Some desperate cases have 

 received 100,000 units and have recovered. The following is the 

 very good guide given by Park: 



