5i6 THE POPULAR SCIENCE MONTHLY. 



duced immunity by injecting a culture of diphtheria bacilli in a 

 broth of thymus gland, after having heated it at 65 to 70 C. 

 (149 to 158 F.) for a quarter of an hour, they having as- 

 sumed that the thymus extract exercised an antitoxic influence 

 on the specific diphtheria toxine. Roux and Vaillard immunized 

 animals by a mixture of three parts of toxine and one part of 

 Gram's solution of iodine, the substances being mixed a few mo- 

 ments before they were injected beneath the animal's skin. Roux 

 found that a rabbit of medium weight easily supported an injec- 

 tion of half a cubic centimetre of that liquid, and after a few 

 days the injection could be renewed and so continued during a few 

 weeks, when the injection would be increased in quantity or the 

 pure toxine might be administered. He also found that it was 

 necessary to frequently weigh the animals and to interrupt the 

 injections when they lost weight, otherwise a depraved condition 

 of the animal's system developed, that might terminate fatally. 

 Animals thus immunized may be injected with a dose of toxine, 

 or a quantity of culture of virulent bacillus that would ordinarily 

 be fatal with but little if any unpleasant efi^ect. 



In 1890 Behring demonstrated the fact that blood-serum taken 

 from an immunized animal was capable not only of producing 

 immunity from the same infectious principle in another animal, 

 but, further, that it possessed the power of curing an infection 

 already in progress. This latter remedial employment of serum 

 containing some antitoxine is called serum therapy. The serum 

 is called an antitoxine serum because it contains some agent that 

 antagonizes the toxine. 



Besides the serum, Ehrlich, Roux, and others found that the 

 milk of goats and cows that had been immunized was a source of 

 antitoxine, though such milk was much less active than the serum. 



The investigators found that of all the animals capable of fur- 

 nishing large quantities of antidiphtheritic serum the horse was 

 most easily immunized. Roux frequently found horses in which 

 the injection of from two to five cubic centimetres of strong 

 toxine beneath the skin provoked only a transient fever and a 

 local swelling that quickly disappeared. The cow and the ass 

 were found to be much more susceptible to the action of the tox- 

 ine. Behring held that the antitoxic properties of the serum fur- 

 nished by an immunized animal were greater in proportion to 

 that animal's sensitiveness to the action of the toxine. But 

 Roux did not consider this an established fact, and since 1892 had 

 employed horses for immunization against diphtheria, because 

 horse serum was not harmful when injected into lower animals or 

 man, and from the jugular vein of a horse large quantities of 

 blood might be obtained from which a perfectly clear serum could 

 be separated. 



