470 IMMUNITY. 



purely antitoxic or purely antimicrobic according to the 

 method by which it is prepared. For example, an anti- 

 toxic serum can be obtained by injecting living diphtheria 

 bacilli into the tissues of an animal, the antitoxic property 

 being in all probability developed by means of toxines 

 formed by the bacilli within the body. Having given this 

 explanation, we shall consider the two kinds of serum 

 separately. 



i. Antitoxic Serum. The best examples are the anti- 

 toxic sera of diphtheria and tetanus, though similar principles 

 and methods are involved in the preparation of the sera 

 protective against ricin and abrin, and against snake poison. 

 We shall here speak of diphtheria and tetanus. The steps 

 in the process of preparation may be said to be the follow- 

 ing : First, the preparation of a powerful toxine. Second, 

 the estimation of the power of the toxine. Third, the 

 development of antitoxine in the blood of a suitable animal 

 by gradually increasing doses of the toxine. Fourth, the 

 estimation from time to time of the antitoxic power of the 

 serum of the animal thus treated. 



1. Preparation of the Toxine. The mode of preparation 

 and the conditions affecting the development of diphtheria 

 toxine have already been described (p. 365). In the case 

 of tetanus, the growth takes place in glucose bouillon under 

 an atmosphere of hydrogen (vide p. 72). In either case 

 the culture is filtered through a Chamberland filter when 

 the maximum degree of toxicity has been reached. The 

 term "toxine" is usually applied for convenience to the 

 filtered (sterile) culture. 



2. Estimation of the Toxine. The power of the toxine 

 is estimated by the subcutaneous injection of varying 

 amounts in a number of guinea-pigs, and the minimum 

 dose which will produce death is thus obtained. This, of 

 course, varies in proportion to the weight of the animal, 

 and is expressed accordingly. In the case of diphtheria, in 

 Ehrlich's standard, the minimum lethal dose is the smallest 

 amount which will certainly cause death in a guinea-pig 

 of 250 grms. within four days. Behring uses the term 



