STANDARDISING OF SERA. 439 



may be obtained in a month or two. In one case the serum 

 obtained by Wood reached the value of 1000 units per c.c. 

 (vide infra). 



4. Estimating the Antitoxic Power of ^ or "standardising" 

 tlie Scrum. This is done by testing the effect of various 

 quantities of the serum of the immunised animal against a 

 certain amount of toxine, conveniently ten times the lethal 

 dose, e.g., i c.c. of toxine, of which .1 c.c. is the lethal dose. 

 Various standards have been used, of which the two chief 

 are that of Behring and Ehrlich and that of Roux. Behring 

 adopts as the unit of immunity i c.c. of a serum of which 

 .1 c.c. protects completely^ from ten times the lethal dose of 

 toxine, the serum and toxine being mixed and injected 

 together. For example, i c.c. of a serum of which .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 600 units or even more. 



Roux adopts a standard which represents the animal 

 weight protected by i c.c. of serum against the lethal dose 

 of virulent bacilli, 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 immunisation of an animal against 

 the toxine, a small quantity of its blood is withdrawn from 

 time to time, and the antitoxic power tested in the manner 

 described above. After a sufficiently high degree of anti- 

 toxic 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. 



1 By this is meant not only that a fatal result does not follow, but also 

 that there is an absence of local swelling. 



