farmers' institutes. 251 



that you may understand it, 1-300 of a grain would kill a man of average 

 weight. Now a drop of water weighs one grain, hence, a dose equal to 

 1-300 of the weight of a drop of water would kill a man, or a dose equal 

 in weight to a drop of water would be sufficient to kill three hundred 

 men. Thus you can understand why some of these diseases are so fatal. 

 When a patient suffering from an infectious disease like diphtheria 

 and untreated by a doctor recovers it is because his system was 

 able to build up in it, a substance which neutralized or destroyed the 

 poison produced by the diphtheria germ. When the poison is neutralized 

 the weapon of the germ is taken away and it becomes harmless like a 

 great many of the harmless germs which we find all around us. Now if 

 we take the diphtheria poison and inject it into a horse in the proper 

 ^iiount we will make the horse sick, but if we do not give him too much 

 he will recover. The next time after he has fully recovered we inject 

 a larger dose and he recovers again. We keep on increasing the dose 

 until we have injected a very large amount. Now if we draw oft" some 

 of the horse's blood and allow it to clot, we shall find that in the straw col- 

 ored fluid which is squeezed out of the clot a substance which neutralizes 

 or destroys the poison from the diphtheria germ. Thus we can take dif- 

 ferent doses of diphtheria poison and find out just how large a dose is 

 required to kill a guinea pig of a certain weight. After having discovered 

 the minimum fatal dose for a guinea pig we take ten times this fatal dose 

 and inject it into a guinea pig. Of course this would mean certain death 

 to the guinea pig. However at the same time we inject a small quantity 

 of this horse's blood serum previously mentioned along with this diph- 

 theria poison. We thus experiment on a large number of guinea pigs 

 until we discover exactly how much of the horse blood serum is required 

 to neutralize ten times the fatal dose for a guinea pig of a certain weight. 

 When the poison is exactly neutralized the guinea pig should not get sick 

 at all. Now a horse thus prepared so that his blood will neutralize or 

 distroy diphtheria poison contains antitoxin in his blood. Therefore diph- 

 theria antitoxin is this horse blood serum placed in small vials and sold to ' 

 the physicians. Enough horse blood serum to exactly neutralize one 

 hundred times the fatal dose for one guinea pig or to save the lives of one 

 hundred guinea pigs each receiving a fatal dose of the poison is called an 

 "immunity unit.^ Now you see vials on the market which contain 2000 

 or even 3000 units of diphtheria antitoxin. Just think what this means. 

 It means that there is sufficient antitoxin in a 3000 unit bottle to save the 

 lives of 3000 times 100 or 300,000 guinea pigs, each receiving a fatal dose 

 of poison. This is not theory, for the only way one can know how many 

 units a vial contains, or the strength of the antitoxin is by actual experi- 

 ments with that antitoxin in guinea pigs. Thus you see why the antitoxin 



