STANDARDISING OF SERA. 473 



of toxine, serum and toxine being mixed, diluted up to 4 

 c.c. and injected together subcutaneously. Ten times the 

 lethal dose was used in testing, and a " normal " antitoxic 

 serum is one of which .1 c.c. neutralises this amount, i.e., 

 of which i c.c. contains an immunity unit. Owing to 

 the difficulty of estimating the occurrence of local infiltra- 

 tion at the site of injection, the prevention of the death of 

 the animal is now used as the indication of neutralisation. 

 Ehrlich now uses 100 times the lethal dose as the test 

 amount of toxine. As a standard in testing, Ehrlich 

 employs quantities of serum of known antitoxic power in 

 a dry condition, preserved in a vacuum in a cool place, 

 and in the absence of light. A thoroughly dry condition 

 is ensured by having the glass bulb containing the dried 

 serum connected with another bulb containing anhydrous 

 phosphoric acid. Thus i c.c. of a serum of w r hich .002 

 c.c. will protect from ten times the lethal dose, will possess 

 fifty immunity units, and 20 c.c. of this serum 1000 

 immunity units. Serum has been prepared of which i c.c. 

 has the value of 800 units or even more. 



Roux adopts a standard which represents the animal 

 weight in grammes protected by i 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 grms. against the lethal dose, i c.c. (i 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 antitoxine 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 small quantity of the blood of the animal is withdrawn 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 anti- 

 toxic sera are prepared in a corresponding manner. 



