116 BACTERIOLOGY FOR NURSES 



Occasionally they find conditions suitable for growth on an abrasion 

 of the skin, in the vulva, or on the conjunctiva. If they are able 

 to develop they secrete during their growth the toxin which de- 

 stroys the epithelial cells, and from this area of infection the poison 

 is absorbed and carried to all parts of the body. Other micro- 

 organisms such as pneumococci and streptococci, which may be 

 harmless on intact healthy membranes, readily grow in the necrotic 

 tissue and may add to the severity of the local lesion and the gen- 

 eral toxic condition. 



Diphtheria bacilli rarely enter the blood stream ; they usually 

 remain localized, and only their toxin affects the susceptible body 

 tissues. The outcome of the infection depends largely upon the 

 amount and the strength of the toxin absorbed and the quantity 

 of antitoxin present in the blood. The amount of tissue involved 

 in the nose or throat is not always an indication of the severity of 

 the disease ; virulent bacilli in a small patch may produce more 

 toxin than less virulent ones occupying a larger area. As a rule, 

 the patient who has most antitoxin, whether naturally present 

 or gained as a result of a previous attack of the disease or an in- 

 jection of antitoxin, will be least affected even though the bacilli 

 be extremely virulent. 



Twenty years ago diphtheria was one of the most dreaded 

 diseases ; it had a mortality of at least 30 per cent. About 1888 

 Roux and Yersin discovered that it was produced by a soluble 

 poison ; two years later von Behring demonstrated that circulating 

 in the blood of all animals recovering from an attack of the disease 

 there was a certain substance, antitoxin, which rendered the poison 

 harmless. It seemed evident that this substance must be elabo- 

 rated by the body cells to save themselves from being attacked 

 by the toxin. The idea was then conceived that if a serum rich 

 in antitoxin could be injected into a person suffering from diph- 

 theria it would afford protection by neutralizing the toxin until 

 the cells of the patient could respond sufficiently to produce their 

 own antitoxin in large enough amounts. At first the results were 

 not as satisfactory as expected because the serum was not powerful 

 enough. By 1896, however, it had been sufficiently perfected to 



