DOSAGE OF DIPHTHERIA ANTITOXIN. 473 



carbolic acid, is usually added to prevent its decomposing. Other 

 antitoxic sera are prepared in a corresponding manner. Some 

 further facts about antitetanic serum are given on page 389. 



Use of Antitoxic Sera. — In all cases the antitoxic serum 

 ought to be injected as early in the disease as possible, and in 

 large doses. In the case of diphtheria 1500 immunity units of 

 antitoxic serum was the amount first recommended for the treat- 

 ment of a bad case, but the advisability of using larger doses 

 has gradually become more and more evident. Sidney Martin 

 recommends that as much as 4000 units should be administered 

 at once, and that if necessary this quantity should be repeated. 

 A strong serum prepared by Behring contains 3000 units in 

 5-6 c.c, but even stronger serum may be obtained. Even very 

 large doses of antitoxic serum are without any harmful effects 

 beyond the occasional production of urticarial and erythematous 

 rashes. Where large quantities of serum require to be admin- 

 istered, as is always the case with antitetanic serum, injections 

 must be made at different parts of the body ; preferably not 

 more than 20 c.c. should be injected at one place. The immu- 

 nity conferred by injection of antitoxic serum lasts a compara- 

 tively short time, usually a few weeks' at longest. 



Sera of Animals immunised against Vegetable and Animal 

 Poisons. — It was found by Ehrlich in the case of the vegetable 

 toxins, ricin and abrin, and also by Calmette and Fraser in the 

 case of the snake poisons, that the serum of animals immunised 

 against these respective substances had a protective effect when 

 injected along with them into other animals. Ehrlich found, 

 for example, that the serum of a mouse which had been highly • 

 immunised against ricin by feeding as described above, could 

 protect another mouse against forty times the fatal dose of that 

 substance. He considered that in the case of the two poisons, 

 antagonistic substances — " anti-ricin" and " anti-abrin " — were 

 developed in the blood of the highly immunised animals. A 

 corresponding antagonistic body, to which Fraser has given the 

 name " antivenin," appears in the blood of animals in the process 

 of immunisation against snake poison. 



These investigations are specially instructive, as these vege- 

 table and animal poisons, both as regards their local action and 

 the general toxic phenomena produced by them, present, as we 

 have seen, an analogy to various toxins of bacteria. 



