THE TOXINS OF THE SALMONELLA GROUP 723 



invasive power for the tissues of mice and of other laboratory rodents. A virulent strain 

 will kill 50 per cent, or more of mice injected intraperitoneally with a dose of 100 bacUh, 

 as compared with the 50-100 miUion that are required in the case of a virulent typhoid 

 bacillus. Mice dying within 2 to 3 days after the injection of a moderate dose of a virulent 

 strain will be found to have succumbed to an acute septicaemia with few obvious lesions ; 

 but mice dymg after the more usual period of 5 to 10 days often show characteristic lesions, 

 including a varying degree of splenic enlargement, often associated with the presence of 

 small necrotic foci, larger and very characteristic necrotic lesions in the liver, and sometimes 

 scattered pneumonic patches in the lungs, associated with a scanty pleural exudate. These 

 lesions have been described in some detail by many observers (see, for instance, SeifFert, 

 Jahncke and Arnold 1928). The spread of infection from the intestine, and the subsequent 

 involvement of the various tissues, have been studied and described by Miiller (1912) and 

 by 0rskov and his colleagues (0rskov, Jensen and Kobayashi 1928, 0rskov and Moltke 

 1928, 0rskov and Lassen 1930). These experiments will be considered in some detail in 

 Chapter 47. 



One other point should be emphasized. The disease produced in the mouse by Salin. 

 typhi shows no tendency to spread by contact from mouse to mouse. The disease 

 produced by Salm. it/ phi -murium is highly contagious, and there are few laboratories that 

 have not experienced serious epidemics of this infection among their normal stock of mice 

 or guinea-pigs. 



Salm. enteritidis. 



It need only be said that this species, particularly the danysz variety, behaves in much 

 the same way as Salm. typhi-miirium. Whether all varieties of Salm. enteritidis are equally 

 pathogenic for small rodents, as judged by experimental infection in the laboratory, we 

 do not know. 



Salm. paratyphi B. 



The main interest of this species, from our present point of view, is that it occupies a 

 position in some ways intermediate between tliat of Salm. typhi and Salm. typhi-murium. 

 It is a natural pathogen of man but not of rodents, but antigenically it is very closely related 

 to the mouse-typhoid bacUlus. When injected into mice it kills them in far smaller doses 

 than does Salm. typhi, though it is less virulent than Salm. typhi-muriwm. When admin- 

 istered by the mouth, as 0rskov and his colleagues have shown, it has a Umited abiUty to 

 invade the tissues and multiply in them ; but it rarely gives rise to fatal infections. 



It is probable that many other species of Salmonella will be found to possess high or 

 moderate virulence for laboratory animals, and in some instances we akeady know this 

 to be the case. Salm. cholerce-suis, for instance, is highly virulent for the rabbit. But the 

 mapping-out of the relative virulence, or pathogenicity, of all the 130 or more species 

 or varieties of Salmonella that have so far been described, and of the new arrivals that 

 may well be imminent, will clearly be a laborious undertaking, and one that is perhaps 

 not very likely to be embarked on in the near future. 



The Toxins oJ the Salmonella Group. — As we have noted above, the injection 

 of killed typhoid bacilli, in adequate dosage, will produce toxsemic death in the 

 usual laboratory animals ; and the " toxins " of the typhoid bacillus were 

 studied by several of the earlier bacteriological workers (Pfeiffer 1894, Sauarelli 

 1894, Chantemesse 1897, Brieger 1902). 



Macfadyen and Rowland (1901, 1903), by grinding typhoid bacilli in the frozen state 

 and subsequently extracting them with 01 per cent. KOH, prepared a solution which 

 was highly toxic for rabbits but only slightly toxic for guinea-pigs. Meyer and Bergell 

 (1907) obtained an extract of typhoid bacilh that was toxic for rabbits by suspending 

 the bacilli from agar cultures in slightly alkaline distilled water, and filtering the extracts 

 through Chamberland candles after they had stood for 48 hours at room temperature. 



