196 BACTERIA PATHOGENIC TO MAN 



guinea-pigs, or they may kill, as we have found in a number of 

 instances, in doses of 2 to 5 c.c. subcutaneously or intraperitoneally 

 injected. Animals are not protected by diphtheria antitoxin from the 

 action of these bacilli. At autopsy the bacilli are usually found more 

 or less abundantly in the blood and internal organs. The fact that 

 large injections of antitoxic serum hastens the death of guinea-pigs 

 injected with these bacilli, has given rise to the notion that injections 

 of antitoxin might be dangerous in persons in whose throats these 

 bacilli were present, either as saprophytes or, possibly, as inciters of 

 slight disease. It is not the antitoxin, but the serum, which in large 

 doses injures the vitality of the guinea-pigs and so slightly hastens 

 death. Any serum has the effect. These bacilli were first described by 

 Miss Davis 1 from my laboratory and later by Dr. Alice Hamilton in 

 1904. In my judgment they present no more reason to avoid giving 

 antitoxin than do the streptococci and influenza bacilli. When patho- 

 genic in man they are usually only feebly so. 



Location of Diphtheritic Inflammations and Virulence of Bacilli. Viru- 

 lent bacilli produce and are found not only in pseudomembranous 

 inflammations of the fauces, larynx, and nasal cavities, but also occa- 

 sionally in membranous affections of the skin, vagina, rectum, con- 

 junctiva, nose, and ear (simple membranous rhinitis and otitis media). 

 From the severity of an isolated case the virulence of the bacilli cannot 

 be accurately determined. The most virulent bacillus we have ever 

 found was obtained from a mild case of diphtheria simulating tonsillitis. 

 Another case, however, infected by the bacillus proved to be very severe. 

 In localized epidemics the average severity of the cases probably indi- 

 cates roughly the virulence of the bacillus causing the infection, as here 

 the individual susceptibility of the different persons infected would, 

 in all likelihood, when taken together, be similar to that of other groups; 

 but even in this instance special conditions of climate, food, or race 

 may influence certain localities. Moreover, the bacteria associated 

 with the diphtheria bacilli, and which are liable to be transmitted 

 with them, may influence the severity of and the complications arising 

 in the cases. It must be remembered that bacilli of like toxic power 

 may differ in their liability to infect. Virulence has thus two distinct 

 meanings when used to describe diphtheria bacilli. 



Virulent Bacilli in Healthy Throats. Fully virulent bacilli have fre- 

 quently been found in healthy throats of persons who have been brought 

 in direct contact with diphtheria patients or infected clothing without 

 contracting the disease. It is, therefore, apparent that infection in 

 diphtheria, as in other infectious diseases, requires not only the pres- 

 ence of virulent bacilli, but also a susceptibility to the disease, which 

 may be inherited or acquired. Among the predisposing influences 

 which contribute to the production of diphtheritic infection may be 

 mentioned the breathing of foul air and living in overcrowded and 

 ill-ventilated rooms, poor food, certain diseases, more particularly 



1 Medical News, April 29, 1899. 



