588 STREPTOCOCCUS 



antigen common to the hsemolytic and non-hsemolytic members of Group D. The observa- 

 tions of Sherman, Smiley and Niven (1940), of Seelemann and Nottbohm 1940) and of 

 Shattock and Mattick (1943) have shown that the lactic streptococci form a group-specific 

 antigen of their own ; and it therefore seems appropriate, in spite of the absence of haemo- 

 lysis caused by these organisms, to include them in the Lancefield series and assign them 

 to Group N. There seems no reason why the chief representative of this group, the 

 properties of which have already been described, should not be awarded specific rank 

 and referred to as Str. lactis. Whether the closely allied organism, called by Orla-Jensen 

 (1919) Sir. cremoris, is to be treated similarly is less clear. According to Yawger and 

 Sherman (1937) it differs from Str. lactis in the sUghtly larger size of its cells, its greater 

 tendency to form chains, its lower optimal temperature, its greater susceptibihty to 

 methylene blue, its failure to form ammonia in a 4 per cent, peptone medium, and certain 

 other minor respects. These differences se«m to be far more suggestive of environmental 

 variation than of fixed hereditary characters, and it would be wise for the present to 

 regard Str. cremoris as no more than a variant of Str. lactis. 



The Classification of the a-hsemolytic Streptococci.— It has been noted in pre- 

 ceding sections that streptococci giving a-haemolysis vs^ith a characteristic green 

 coloration on blood agar plates, failing to produce a soluble hsemolysin, usually 

 fermenting raffinose but not mannitol, and possessing certain other characters in 

 common, can constantly be isolated from the human mouth and throat and from 

 the faeces of cattle. The problem that confronts us is whether these streptococci 

 form a group or a species, and, if a group, whether the species of which that group 

 is formed are sufficiently well differentiated to be allotted specific names. 



Ayers and Mudge (1923) express the view that the a-hsemolytic streptococci of the 

 bovme intestine differ in certain minor characters from the a-hsemolytic streptococci of 

 the human mouth and throat ; and reference to several of the papers quoted above will 

 reveal a tendency to accord the bovine strains specific rank, under the name Str. bovis. 

 It is, however, by no means clear that this procedure is justified, or on what differential 

 characters the jjroposed nomenclature is to be based. Indeed there is some evidence to 

 suggest that Str. bovis may be related to the Group D hsemolytic streptococci (see Shattock 

 and Mattick 1943). 



There is another streptococcus falling into this group that seems to merit separate 

 consideration. Freudenreich ( 1897) isolated a streptococcus from Kefir, a form of fermented 

 milk. This streptococcus has the usual characters of the viridans type (Sherman 1921, 

 Ayers ei al. 1921, Ayers and Rupp 1922). When tested in the ordinary way, with a 

 Durham fermentation tube, this organism, Uke other streptococci, produces acid, but no 

 gas, from various substrates. If, however, it is tested in the Eldridge fermentation tube 

 in which it is grown in a shallow layer of fluid medium, freely exposed to the air, and 

 the CO2 evolved is taken up by a standard solution of barium hydroxide, exposed in a 

 connected tube of the same kind, as large an amount of COg is evolved from lactose as is 

 given off when that sugar is fermented by Bact. coli. It would seem that the almost 

 anaerobic conditions existing in the closed Durham fermentation tube inhibit the produc- 

 tion of CO2 by the Kefir streptococcus. It is difficult to assess the real significance of this 

 observation, since we have no knowledge of the way in which most species of non-gas - 

 producing bacteria would behave if tested in the Eldridge tube, mstead of in the closed 

 Durham, or Smith, tubes in which they have in fact been tested ; but no COj was formed 

 in the Eldridge tube by such other strains of streptococci as were tested by Ayers and 

 his colleagues, including strains isolated from the bovine faeces, and the lactic acid 

 streptococcus. 



There can, we think, be little doubt that the a-hsemolytic streptococci of the 

 viridans type will ultimately be separated into a number of distinct species or types ; 



