428 THE QUESTION OF IMMUNITY AND ANTITOXINS 



conveys the blood from the cannula to pass through. The tube, 

 therefore, passes through the metal lid and two paper covers, which 

 it was made to pierce. When enough blood has passed into the 

 vessel the tube is withdrawn, and the metal lid slightly turned. 

 Thus the contained blood is protected from the air.* The jar con- 

 taining the blood (which contains the antitoxins) is next placed in 

 a dark, cool cellar, where it stands for separation of the clot. During 

 this time the blood naturally coagulates, the corpuscles falling as a 

 dense clot to the bottom, and the faintly yellow serum rising to the 

 top. The serum, or liquor sanguinis, averages about 50 per cent, of 

 the total blood taken. Sometimes antiseptic ('3 per cent, carbolic 

 acid) is added with a view to preservation. It is generally filtered 

 (through a Berkefeld) before bottling for therapeutic use, and 

 examined bacteriologically as a test of purity, for sterility and for 

 absence of toxicity, and for antitoxic value. 



The latter step is the estimation of the antitoxic power of the 

 serum, or what is termed the " standardising " of the serum. This 

 is accomplished by testing the effect of various quantities upon a 

 certain amount of toxin. Ehrlich has adopted as the immunity unit 

 the amount of antitoxic serum which will neutralise a hundred times 

 the minimum lethal dose of toxin, the serum and toxin being mixed 

 together, diluted up to 4 c.c, and injected subcutaneously. A normal 

 antitoxic serum is one of which 1 c.c. contains an immunity unit. 



Process of Standardisation of Antitoxins. — This matter will be 

 best illustrated by an illustration, as follows : — 



Utage 1. — Varying amounts of a toxin are added to a definite amount of antitoxin, 

 i.e. to 1 Ehrlich unit, and injected into a guinea-pig of 250 grammes. That mixture, 

 which kills the guinea-pig in four days, is held to contain 1 M.L.D., over and above 

 the amount of toxin required to neutralise 1 antitoxin unit. The total amount of 

 toxin used to bring about the death of the guinea-pig in four da,ys = the standard 

 toxin for that particular standardisation. 



Stage 2. — -Varying quantities of the antitoxin to be tested are added to the 

 standard toxin and injected into guinea-pigs. That mixture, which kiUs the guinea- 

 pig in four days as before, contains 1 M.L.D. of toxin over and above that 

 neutralised by the added antitoxin. The amount of toxin used in Stages 1 and 2 

 is the same, therefore the amount of antitoxin in Stages 1 and 2 must be equal. In 

 Stage 1, 1 Ehrlich unit was used, therefore the amount of antitoxin in Stage 2 which, 

 with the standard toxin killed the guinea-pig in four days, also contains 1 Ehrlich unit. 



Example. Stage 1. 



•25 c.c. Toxin + 1 Ehrlich Antitoxin Unit . Guinea-pig alive fifth day. 



'Zo c.c. ,, ,, ,, . ,, ,» 



•27 c.c. ,, ,, ,, . „ died fourth day. 



•28 C.C. ,, „ ,, . ,, died first day. 



.'. ^27 C.C. Toxin = Standard toxin, containing 1 M.L.D. of toxin after neutral- 

 isation with 1 Antitoxin unit. 



* At the conclusion of the operation the cannula is removed from the jugular vein 

 and the wound is closed by the valvular character of the slit in the skin and vein, 

 and the elasticity of the wall of the vein. No stitching or dressing is required. 



