434 MICROORGANISMS 



ened) cultures of the bacteria and later with more virulent 

 cultures. After the rabbits had been treated in this way, 

 they were completely immune from the disease. Next, 

 these experimenters discovered that the blood serum of the 

 immunized rabbits, when injected into other rabbits that 

 had been inoculated with virulent cultures of the bacteria, 

 had the power of neutralizing or destroying the toxine pro- 

 duced by the bacteria. In other words, they had discovered 

 that the blood serum of immunized rabbits contained some 

 substance which destroys the toxine of the diphtheria bacteria 

 and which, when present in the blood of an animal, protects 

 the animal against the toxine. It is thought that in some 

 way, the diphtheria toxine stimulates the body of the animal 

 to produce this neutralizing substance or antitoxine, as it is 

 called. Since these first experiments, it has been found that 

 the body of an animal can be caused to produce the anti- 

 toxine by merely injecting into it some of the sterile toxine which 

 has been freed from the bacteria. 



504. Preparation of the Antitoxine. The antitoxine now in 

 use in the treatment of diphtheria is manufactured in the 

 bodies of horses. The methods by which this is done are of 

 the most careful and painstaking kind and every possible 

 precaution is taken to insure the purity and safety of the 

 product. In the first place, perfectly healthy, horses are 

 secured and they are surrounded with every condition con- 

 ducive to continued good health. When found to be perfectly 

 healthy by the most searching examination, a small fraction 

 of a cubic centimeter of sterile broth culture, containing a 

 standard quantity of diphtheria toxine is injected under the 

 skin of the horse. This causes some fever and swelling at 

 the point of injection but the horse soon recovers and is able 

 to stand a stronger dose the next time. The dose of toxine 

 is gradually increased as fast as the condition of the horse 

 will permit until as much as from 300 to 500 c.c. of the broth 

 containing the toxine are injected at one time. The reason 

 that the horse can stand gradually increasing doses, lies in 



