268 THE DIPHTHERIA BACILLUS 



hour old culture of the diphtheria bacillus which was certainly fatal to control 

 animals. 



[Thus if 0*01 c.c. of a serum would immunize a guinea-pig weighing 500 grams 

 against 10 times the lethal dose of a 48 hour old culture of a virulent diphtheria 

 bacillus, it follows that O'l c.c. would be required to immunize 5,000 grams. That 

 amount then was the unit and 1 c.c. of the serum would contain 10 units.] 



3. Ehrlich adopted another unit of measure. The unit of antitoxin (I.E.) 

 is the amount of antitoxin necessary to neutralize 100 minimal lethal doses 

 of normal toxin (i.e. of a toxin which is fatal to guinea-pigs in doses of 0*1 c.c.). 

 Thus if O'Ol c.c. of a given serum neutralizes 100 fatal doses of toxin that 

 serum is said to contain 100 antitoxic units per c.c. 



It was difficult to get comparable results by this method because the 

 toxicity of a given toxin diminishes with the lapse of time. On the other 

 hand the antitoxin content of a carefully standardized serum dried in vacua 

 and without heating is known to remain constant almost indefinitely. 

 Ehrlich therefore having determined an antitoxic unit (as above) prepares a 

 glycerin solution of the serum containing 17 units per c.c. This preparation 

 is now used in antitoxin laboratories as the standard for testing serums. 

 One c.c. of Ehrlich's glycerin solution diluted with 16 c.c. of water gives a 

 solution containing 1 unit of antitoxin per c.c. 



It is then easy to titrate a toxin against the standard antitoxin and after 

 standardizing the toxin very carefully the latter is used to titrate the anti- 

 toxin under investigation. 



4. The French method of standardizing antitoxin. Roux prefers to 

 standardize antitoxin according to its preventive strength (pouvoir preventif). 

 The preventive strength is the numerical ratio between the weight of a given 

 animal guinea-pig in grams and the amount of serum necessary to save 

 its life if it be inoculated 12 hours later with 0*5 c.c. of a young and highly 

 virulent culture. For example, if the guinea-pig weigh 500 grams and O'l c.c. 

 of serum has to be inoculated to protect it against the subsequent inoculation 

 of culture the preventive strength is , and the serum is said to be active 



in 1 1 



111 5,000' 



In practice the Ehrlich and Roux methods may usefully be controlled 

 against each other ; for instance, a serum is said to contain 100 antitoxic 

 units per c.c. and to have a preventive strength of 50 .Q 0( j. It must be borne 

 in mind however, that the maximum of preventive strength may not coincide 

 with the maximum of antitoxic strength (Martin, Momont and Prevot). 



A serum which has a preventive strength of 50 * 00 is suitable for the 

 treatment of diphtheria in man, but a more powerful serum ( 70 * 00 or even 

 100^000) i s eas ily prepared. The serum made at the Pasteur Institute with 

 the older toxins contained 100 antitoxic units per c.c. and had a preventive 

 strength of 50 Q OO ; but at the present time, using toxins prepared by growing 

 the bacillus in Martin's broth which are ten times stronger than the older 

 toxins, the serum supplied contains at least 200-300 antitoxic units per c.c. 

 and has a preventive strength of 7-00700 - 



(d) Serum therapeutics. 



The application of serum therapy to the treatment of diphtheria in the 

 human subject has yielded results which might have been expected from 

 animal experiment. The serum therapy of diphtheria is one of the most 

 striking successes of modern therapeutics. 



1 Animals treated in this way do not survive indefinitely but die generally in from 

 1-6 months (Roux). 





