DIPHTHERIA BACILLUS 85 



to kill it. In water it lives a short time, and exposure to sunlight destroys it 

 in several weeks. When dried and protected from sunlight it survives in dust, 

 etc., for many weeks. Carbolic acid, i per cent, solution kills the diphtheria 

 bacillus in less than 2 minutes; it is equally sensitive to other chemical germicides. 



Toxin. The diphtheria bacillus produces a powerful extracellular toxin'. 

 Different strains of the organism vary in this respect, some forming little and 

 others much toxin. Alkaline veal infusion broth is the best medium in which 

 to obtain toxin and it is best produced when incubation is maintained in a moist 

 atmosphere between 35C. and 37C. For toxin production an abundant 

 supply of oxygen (air) is required. 



Diphtheria toxin is filterable, hence after the bacillus has produced toxin 

 in bouillon, by filtering the culture through an unglazed porcelain tube the toxin 

 is recovered in the filtrate free from bacteria. As small an amount as J^oo cc. 

 of such a filtrate often contains sufficient toxin to kill a guinea-pig. 



Stored in a cool dark place diphtheria toxin gradually deteriorates in the 

 course of months; heating above 58C. rapidly attenuates it, iooC. destroys 

 in a short time. 



The diphtheria toxin is water-soluble and alcohol-insoluble. 



By injecting subcutaneously varying amounts of toxin into different guinea- 

 pigs of the same weight the lethal dose can be determined. 



A subcutaneous injection of a very small fraction of the lethal dose of anti- 

 toxin acts on some animals in such a way as to increase resistance in 5 to 10 

 days; a second injection of a quantity of toxin 50 to 100 per cent, greater than 

 given at first will then further increase the animal's resistance and by continu- 

 ing the treatment, giving subcutaneous injections of progressively larger doses 

 of toxin at intervals of about a week until from 6 to 12 injections have been 

 administered, a high degree of resistance or immunity is conferred upon the 

 animal. 



Blood serum obtained from an animal so immunized when mixed with 

 diphtheria toxin neutralizes it, makes it inert, and deprives it of disease-producing 

 power. Such serum is known as diphtheria antitoxin and is used in the treat- 

 ment of diphtheria. Serum obtained from animals immunized against diph- 

 theria toxin does not contain agglutinins or amboceptors. 



Agglutination tests and complement fixation tests are not available in the 

 diagnosis of diphtheria, nor to differentiate diphtheria bacilli from pseudo- 

 diphtheria bacilli. 



Pathogenesis. The diphtheria bacillus has a selective affinity for the mu- 

 cous membranes of man, especially the mucosa of the upper air passages. This 

 organism may be found upon the mucous membrane of the throat, tonsils or 

 nose of healthy people who have never had the disease; this is a common occur- 

 rence among those in contact with diphtheria patients and relatively rare 

 among other healthy persons. Healthy persons who harbor the diphtheria 

 bacillus, so called carriers, are dangerous, and may transmit the bacilli to others 

 in whom the organisms promptly cause disease. Epidemics of diphtheria 

 have been traced to such sources, especially among school children. 



