570 PATHOGENIC MICROORGANISMS 



change has been found, MacCallum states that "the changes in the 

 adrenals are likely to be more intense than in most of the other organs, " 

 showing hemorrhages and cellular degeneration. This may have direct 

 bearing on the abnormal fall in blood pressure. There is a marked 

 action on the part of the diphtheria toxin upon nerve tissues, both 

 neurons and cells. This results in post-diphtheritic paralyses which 

 occur particularly in cases that have been insufficiently or not at all 

 treated with antitoxin. The paralyses are particularly frequent in the 

 areas supplied by the cranial nerves and among the most common forms 

 are paralysis of the muscles of the soft palate of the larynx and the ocular 

 muscles. Paralysis, however, may also appear in other parts of the 

 body. We have seen several cases where a sore throat was not sus- 

 pected of being diphtheria until late paralysis had occurred. 



For the usual laboratory animals the diphtheria bacillus is highly 

 pathogenic. Dogs, cats, fowl, rabbits, and guinea-pigs are susceptible. 

 Rats and mice are resistant. False membranes, analogous to those 

 found in human beings, have been produced in many animals, but only 

 when inoculation had been preceded by mechanical injury of the 

 mucosa. Small quantities (0.5 to 1 c.c.) of a virulent broth culture, 

 given subcutaneously to a guinea-pig, may produce the greatest symp- 

 toms and within six to eight hours the animal may show signs of great 

 discomfort. Death occurs usually within thirty-six to seventy-two 

 hours. Upon autopsy the point of inoculation is soggy and serosan- 

 guineous exudate; neighboring lymph-nodes are edematous. Lungs, 

 liver, spleen, and kidneys are congested. There may be pleuritic and 

 peritoneal exudates. Pathognomonic is a severe congestion of both 

 suprarenal bodies. The gastric ulceration recently described by Rose- 

 nau and Anderson 15 may occur, but are by no means regularly found 

 (two out of fifty in our series). 16 



Determination of Virulence. When diphtheria or diphtheria-like 

 bacilli are isolated from the throats of patients not showing typical 

 clinical diphtheria, or from healthy individuals suspected of being 

 carriers, it is important to determine whether these organisms are 

 toxin producers. The usual criterion is their virulence for guinea-pigs. 

 Two c.c. of a forty-eight-hour broth or ascitic broth culture are injected 

 subcutaneously into a normal guinea-pig. This dose will kill the pig in 

 three to five days if the culture is virulent. A control injection should 



ln Eoscnau and Anderson, Jonr. Inf. Bis., iv, 1907. 

 16 Zinsser, Jonrn. Mod. Res., xvii, 1907. 



