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The data to be presented here bear primarily on the relationships of six types of cultures, derived from clover or pea nodules, or stock cultures of Rhizobium trifolii or R. leguminosarum. These six types, while they were derived from sources which might lead one to suspect their identity with the clover and pea nodule organisms, nevertheless possessed cultural characteristics markedly different from those of the rhizobia. A number were chromogenic, and some produced only negligible amounts of gum. These facts were considered worthy of further investigation, for they pointed to the possibility of radical changes in the root-nodule organisms which, if properly understood, might help to explain the sudden losses in infective power which are known to occur and the fluctuations in nitrogen-fixing ability when in association with leguminous plants. The transformations, one to another, of the six abnormal types of organisms and of the normal type as treated in this paper, coupled with the presence of filterable forms, are suggestive of dissociation phenomena as described by those who have worked with other organisms. Previous citations of cultural variation however among the species of Rhizobium have been few. With minor modifications, only one type of colony for each crossinoculation group has been recognized. Deviations from these types have usually been looked upon by other workers as contaminations. The only unquestioned description of a rough form is that of Israilsky and Starygin (1930). No intermediates are mentioned. Our cultures do not conform to their description of a rough race.

Typhoid fever is still a public health problem of considerable importance in many parts of the world. Any contribution to our fund of knowledge concerning the etiologic agent (applicable to diagnosis, prophylaxis, and therapy) is, therefore, to be welcomed as a possible basis for better control of the disease. The discovery by Felix and Pitt in 1934 (30, 31) of a hitherto undescribed antigenic component of the organism responsible for the disease was a step in this direction. Up to that time Eberthella typhosa was known to contain at least two heat-stable antigens in the somatic fraction and one specific antigen in the flagellar fraction. The toxic manifestations of typhoid fever were commonly thought to be due to the endotoxins contained in the somatic fraction. An additional property of the organisms, virulence (at least for mice), was now described as being associated with the presence of the new-found component, and it was accordingly named "Vi". It was this concept of the antigen being a virulence antigen which gave such pronounced impetus to renewed study of the typhoid organism; for the implications concerning severity of attack and immunity were quickly seen. The purpose of this review is to take bearings on how much progress has been made as a result of the studies thus stimulated, and to call attention to places where a strengthening of evidence would be desirable.Occurrence. Almost all freshly isolated typhoid cultures have been shown to contain the Vi antigen (29,46,20,1,66,57). In addition, it has been found sporadically in some of the Hirschfeld paratyphoid C strains (46), in a species of Salmonella designated as "ballerup" (49), and in a few cultures of the coli group (48).Strains of Eberthella typhosa which possess the antigen do not differ noticeably in cultural reactions (including fermentative ability) from those which lack it, although Giovanardi (36) reports that colonies of the Vi-containing form are somewhat more opaque than those of the forms not containing it.Properties. The antigen has been precipitated from protein-free trichloracetic acid extracts by uranyl salts (13, 59). Freeman and Anderson (34) were unable to repeat this separation from the 0 complex and hence are not convinced that the Vi properties may be ascribed to a compound separable from the 0 fraction. However, Henderson (43) demonstrated at least part of the Vi substance free from any of the smooth 0 substance in anhydrous diethylene glycol extracts of rough Vi-containing forms.Acetone extracts containing Vi and 0 fractions show a precipitation reaction with phosphotungstic acid in 5% sulphuric acid and with neutral lead acetate, uranium acetate, mercuric acetate and aluminum sulphate, whereas extracts containing only the 0 fraction fail to show precipitates with these reagents (65). The antigen is probably situated for the most part near the surface of the 43 on July 6, 2020 by guest