PARASITES 433 



diagnosis of the disease and enables a physician to de- 

 termine with certainty when a patient may safely be freed 

 from quarantine. The organism grows readily on several 

 different kinds of culture media and grows abundantly in 

 milk if kept at a suitable temperature. This latter fact is 

 an important factor in the spread of the disease and a good 

 many epidemics have been known to be caused by the hand- 

 ling or distributing of milk by some person suffering with a 

 mild attack. 



The organism is not known to form spores but it has a 

 rather high resistance to drying and has been known to live 

 and retain its virulence for several months in dried mem- 

 brane or sputum. This makes necessary the disinfection of 

 houses in which cases have occurred. 



502. Nature of the Toxine. When the bacteria are grown 

 in a nutrient broth, a soluble toxine is produced in the broth. 

 This may now be passed through a fine porcelain filter which 

 effectively separates the bacteria from the broth containing 

 the toxine in solution. This sterile toxine, when injected into 

 the body of a susceptible animal, produces all the symptoms 

 of the disease except the false membrane in the throat. The 

 false membrane is caused, in a normal case, by the bacteria 

 themselves together with certain fibrinous excretions of the 

 mucous membrane. Since the bacteria are not present in 

 the body of a healthy animal inoculated with the sterile 

 toxine, the membrane does not form. 



Little or nothing is known of the chemical nature of the 

 toxine or of the manner of its production. It is only known 

 that it is a powerful poison which is thrown out from the 

 bodies of the bacteria and which attacks certain tissues of 

 the animal body. 



503. The Antitoxine. In 1890, BEHRING and KITASATO 

 took the next step in the mastery of this disease by discovering 

 a method of producing an ANTITOXINE which is both a cure and 

 a preventive for this disease. They experimented with 

 rabbits by first inoculating them with attenuated (weak- 



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