igg METHODS OF SERO-DIAGNOSIS. 



the poisonous principles being Ricin, Abrin and Robin respec- 

 tively; and following this, in 1894, Calmette produced similar 

 effects by the injection of certain snake-venins. Tn a similar 

 way antiferments have also been produced by injecting animals 

 with various ferments, such as Emulsine, Rennin, Pepsin and 

 many others. Other antitoxic sera have been produced since 

 then. 



At the present time it is not definitely known how the direct 

 neutralizing effect, which is seen on injecting the toxic body and 

 its respective antibody, either separately and at about the same 

 time or after they have been mixed together, is brought about. 

 Ehrlich believes that the union of toxin and antitoxin is of a 

 chemical nature, whilst Bordet and others suggested that it could 

 be regarded as an adsorption phenomenon occurring between two 

 colloid substances. 



The facts in favour of these theories will not be reviewed 

 here, but the outcome of researches made in attempting to settle 

 this question, was to furnish us with a method for the standardi- 

 zation of the powers of antitoxins, also the formation of theories 

 regarding the nature of the re-action of the animal body to the 

 action of toxins, and the further extension of these theories to 

 include reactions to antigens of other natures. 



The method adopted for the standardization of the anti- 

 toxins of Diphtheria and Tetanus in general use at the present 

 time is to estimate, in the first instance, the smallest quantity of 

 the toxin necessary to kill a guinea-pig. weighing 250 grammes, 

 in from four to five days, this dose being known as the " minimum 

 lethal dose " of the toxin. The quantity of antitoxic serum 

 which, when mixed with 100 such minimal lethal doses of toxin, 

 is sufficient to neutralize the toxin and prevent the death of the 

 guinea-pig within the given time is spoken of as the " immunity 

 unit " or " antitoxin unit," and when one knows what this quan- 

 tity is, it is easy to calculate how many immunity units are 

 present in one cubic centimetre of a given serum. 



In standardizing antitoxins it will be seen from the above 

 that one must possess either a standard toxin or antitoxin, and 

 it is the latter which is used. It is prepared, in a dry form by 

 dessication over anhydrous phosphoric acid in vacuo, in a dark 

 cool place, and issued from certain well-known laboratories. 

 Using a solution of this powder, the neutralizing value of a given 

 toxin can be ascertained against it, and the neutralizing effect of 

 the antitoxin whose power is to be determined is then estimated 

 against this same toxin, and thus the antagonizing powers of the 

 standard antitoxin and that under examination can be compared. 



The study of the toxin-antitoxin reaction led Ehrlich to 

 believe that toxin really contained other bodies, to which he gave 

 the names toxons and toxoids, all possessing varying affinities 

 for antitoxin, and also led him to formulate his famous "side 

 chain theory " of immunity, which though not accepted bv all 

 workers in immunity, nevertheless acts as a working hypothesis 

 in regard to serum-immunity, and by furnishing ideas which 



