PSEUDODIPHTHERIA. 143 



is extracted from the immunized horse at one time, collected 

 in well-sterilized vessels, and allowed to clot in an ice-chest 

 for two or three days, after which the clear serum is pipetted 

 off and stored in sterilized flasks, the antiseptic strength of 

 the serum being properly labelled on each flask. This anti- 

 V toxin power, called units, is estimated as follows : 



Ten times a fatal dose of a toxin, that is known to kill a 

 ^-250-gram guinea-pig within three days, is mixed with differ- 

 ent quantities of the serum to be tested, say, 0.10, 0.01, 

 0.001 c.c., and these mixtures injected into different guinea- 

 pigs, Nos. 1, 2, and 3, respectively. Should guinea-pig No. 1 

 survive the mixed injection, and guinea-pigs Nos. 2 and 3 

 die, the antitoxin is said to contain 10 times 10 units in 1 c.c. ; 

 that is, it is an antitoxin of 100-unit power. Should guinea- 

 pigs 1 and 2 survive, the antitoxin is one which in 1 c.c. has 

 protecting powers amounting to 10 multiplied by 20, or 200 

 antitoxin units. Should guinea-pig No 3 also survive this 

 injection, then the serum used is equivalent to 10 times 100, 

 or 1000 antitoxin units per c.c. 



No serum should be accepted for use in the treatment of diph- 

 theria unless its immunizing or antitoxic power is equivalent to 

 at least WO units per c.c.; a serum used as a protective only 

 may be accepted with 100 units antitoxic power per c.c. 



In order to test the antitoxin and for the purpose of im- 

 munizing animals, it is necessary to produce toxins of a 

 standard virulence. This, as has been seen, is not always a 

 task of easy performance. The standard of toxins accepted 

 in all laboratories and establishments in which antitoxin is 

 manufactured is a toxin of which 0.10 c.c. is able to kill a 

 250- or 300-gram guinea-pig within three days, and no toxins 

 should be used excepting such as have this power. It is best 

 manufactured by growing virulent cultures of Bacillus diph- 

 therias in large Erlenmeyer flasks, with free access of air and 

 at a temperature of 37 C. The height of the toxicity of 

 the culture is reached in about eight to ten days, when the 

 culture should be removed from the incubator and filtered 

 through a Chamberlain porcelain filter, tested on guinea-pigs, 

 and if found of the required strength put away in sterile 



