How Science Helps the Body 161 



most important is the antitoxin of diphtheria. 

 This is prepared from the horse. It is not 

 necessary to cause the horse to endure 

 diphtheria, as we know it, at all. For if 

 the poison which the diphtheria bacillus 

 sets free, when it is grown in beef -tea cultures 

 in the laboratory, with all the germs filtered 

 off, be put into the horse, his cells get to work, 

 just as ours do when we have the disease, 

 diphtheria, and just as his would if the bacilli 

 were allowed to grow in his body. Presently 

 antitoxin begins to mingle with his blood. 



The horse lends himself readily at first to 

 small, then to increasing doses of the potent 

 diphtheria poison. He becomes readily im- 

 mune and he is so big that he furnishes a large 

 amount of blood without apparent inconven- 

 ience. When the animal is poison proof, no 

 longer showing any ill effects to doses of the 

 toxin so large that if given at first they would 

 have been inevitably fatal, he is bled from 

 a large vein in the neck. The blood is set 

 in a cool place and clots, clear fluid, the serum, 

 separating from the rest. This yellowish 

 clear serum contains the antitoxin. 



