USE OF ANTITOXIC SERA 469 



the lethal dose, will possess 50 immunity units, and 20 c.c. of 

 this serum 1000 immunity units. Sera have been prepared of 

 which 1 c.c. has the value of 800 units or even more. 



Roux adopts a standard which represents the animal weight in 

 grammes protected by 1 c.c. of serum against the dose of virulent bacilli 

 lethal to a control guinea-pig in thirty hours, the serum being injected 

 twelve hours previously. Thus, if '01 c.c. of a serum will protect a 

 guinea-pig of 500 grins, against the lethal dose, 1 c.c. (1 grm.) will protect 

 50,000 grms. of guinea-pig, and the value of the serum will be 50,000. 



During the process of development of antitoxin a small 

 quantity of the blood of the animal is withdrawn from time to 

 time, and the antitoxic power tested in the manner described 

 above. After a sufficiently high degree of antitoxic power has 

 been reached the animal is bled under aseptic precautions, and 

 the serum is allowed to separate in the usual manner. It is then 

 ready for use, but some weak antiseptic, such as - 5 per cent 

 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 p. 384. 



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 anti- 

 toxic serum was the amount first recommended for the treatment 

 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 uaits 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 sera 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 ad- 

 ministered, 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 immunity 

 conferred by injection of antitoxic serum lasts a comparatively 

 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 



