VARIATIONS IN VIRULENCE OF B. DIPHTHERIA 421 



Toxic bodies have also been obtained from the tissues of those 

 who have died from diphtheria. Roux and Yersin, by using 

 a filtered watery extract from the spleen from very virulent cases 

 of diphtheria, produced in animals death after wasting and 

 paralysis, and also obtained similar results by employing the 

 urine. The subject of toxic bodies in the tissues has, however, 

 been specially worked out by Sidney Martin. He has separated 

 from the tissues, and especially from the spleen, of patients who 

 have died from diphtheria, by precipitation with alcohol, chemical 

 substances of two kinds, namely, albumoses (proto- and deutero-, 

 but especially the latter), and an organic acid. The albumoses, 

 when injected into rabbits, especially in repeated doses, produce 

 fever, diarrhoea, paresis, and loss of weight, with ultimately a 

 fatal result. He further found that the paresis is due to 

 well-marked changes in the nerves. Substances obtained from 

 diphtheria membrane have an action like that of the bodies 

 obtained from the spleen, but in higher degree. Martin con- 

 siders that this is due to the presence in the membrane of an 

 enzyme which has a proteolytic action within the body, resulting 

 in the formation of poisonous albumoses. 



Immunity. This is described in the general chapter on 

 Immunity. It is sufficient to state here that a high degree of 

 immunity, against both the bacilli and their toxins, can be 

 produced in various animals by gradually increasing doses either 

 of the bacilli or of their filtered toxins (vide Chapter XXII.). 



Variations in the Virulence of the Diphtheria Bacillus. In 

 cultures on serum the diphtheria bacilli retain their virulence 

 fairly well, but they lose it much more quickly on less suitable 

 media, such as glycerin agar. Roux and Yersin found that, 

 when the bacilli were grown at an abnormally high temperature, 

 namely, 39*5 C., and in a current of air, the virulence diminished 

 so much that they became practically innocuous. They also 

 found that the virulence could often be restored if the bacilli 

 were inoculated into animals along with streptococci, inocula- 

 tion of the bacilli alone not being successful for this purpose. 

 If, however, the virulence had fallen very low, even the presence 

 of the streptococci was insufficient to restore it. The virulence 

 is tested by the amount of living bacilli necessary to produce a 

 fatal result on injection into a guinea-pig, and is to be dis- 

 tinguished from the power of producing toxin in a fluid medium ; 

 as pointed out by Dean, the two properties often do not 

 correspond, Arkwright has found that the virulence of recently 

 isolated strains varies enormously, as much as in a proportion of 

 1 to 400. Some non-virulent diphtheria bacilli have been found 



