796 HEMOPHILUS 



influenza bacillus, since this character serves to divide the species into two distinct 

 types. 



Pritchett and Stillman (1919) noted the occurrence, among a large sample of cultures 

 of hsemophiljc bacilli isolated from cases of influenza and from normal persons, of a small 

 proportion of strains which produced a well-defined zone of haemolysis on blood agar. These 

 strains were morphologically of the bacillary or thread type. They were studied in greater 

 detail by Stillman and Bourn ( 1920) ; and their occurrence has been noted by many sub- 

 sequent workers. Kristensen (1922) studied several strains of these haemolytic bacilli, 

 and noted that some of them seemed less dependent on the presence of haemoglobin than 

 H. infvenzce. On the other hand, the majority of his strains showed well-marked satel- 

 litism ; thus demonstrating their dependence on the V factor. Fildes ( 1924) found that 

 13 of 14 hsemolytic strains grew in the presence of the V factor alone. In morphology these 

 strains are, for the most part, definitely atypical, showing numerous threads, and coarser 

 baciUary forms than are commonly encountered in H. influenzae itself. The colonies 

 produced by these strains tend to assume the characters which Kristensen regards as 

 atypical, being more opaque and more friable than the typical form. Another striking 

 characteristic of these haemolytic strains is their tendency to die out in subculture, a 

 character which has been noted by subsequent observers (Dible 1924). Kristensen notes 

 that the power to cause haemolysis is maintained unaltered by those strains which survive 

 artificial cultivation for considerable periods ; and that there is no tendency for other 

 strains to acquire this property. Dible (1924) studied 67 strains of haemophilic bacilli 

 isolated from the nasopharynx of normal persons, and found 14 of them to be haemolytic. 

 Five of these strains resembled the cocco- bacillary form of H. influenzce, with the single 

 exception that the bacilh were a little larger, and rather more definitely bacillary : the other 

 9 were atypical, in formmg larger colonies, giving a flocculent growth in broth, or departing 

 widely from the cocco-bacillary form. Valentine and Rivers ( 1927) report that the majority 

 of these haemolytic strains require the V factor only for their growth, while a minority 

 require both the X and V factors ; a proportion of non-haemolytic strains of haemophilic 

 bacUh require the V factor only. Valentine and Rivers proposed the name H. para- 

 influenzce for the haemophihc organisms requiring only V factor, irrespective of haemolysin 

 production. It is clear from their descriptions that organisms resembling Pfeiffer's bacUlus 

 in cultural characters and growth requirements may or may not form haemolysin. We 

 propose to adopt their nomenclature, and distinguish H. para-influenzoe from H. influenzce 

 by X and V factor requirements and sub -divide each if necessary into haemolytic and 

 non-haemolytic varieties (see Miles and Gray 1938). 



Biochemical Activities. — The study of the fermentation reactions of H. influ- 

 enzce, and of other haemophilic bacilli, has been retarded by the difficulty experi- 

 enced in preparing a medium which allows of copious growth, and has, at the 

 same time, the transparency and absence of colour which are essential, if changes 

 in hydrogen-ion concentration are to be detected by the usual methods. Some 

 of the media which have been devised within recent years are, however, well 

 adapted for this purpose. 



Levinthal (1918) added various carbohydrates to the agar medium which he devised, 

 tinted it with litmus, and tested the fermentative ability of several strains of H. influenzce. 

 He noted acid production from glucose, but not from laevulose, lactose, mannitol or maltose. 

 Messerschmidt, Hundeshagen and Scheer (1919), using a similar technique, noted slight 

 acid production in glucose, but not in mannitol, lactose, or saccharose. 



Stillman and Bourn (1920) employed a liquid medium prepared by adding an extract 

 of boiled rabbit blood to peptone water, and carried out a careful series of tests on 119 

 strains of //. influenzce and 29 haemolytic strains. More than 90 per cent, of the 119 non- 

 haemolytic strains produced acid from dextrose and galactose, and reduced nitrates ; 73 

 per cent, produced acid from laevulose, and about 25 per cent, from maltose, saccharose 



