CH. iv] VARIATIONS IN MORPHOLOGY 43 



of a spindle or rod, in which case it was difficult to distinguish 

 it from B. diphtheriae. At the same time its tendency to 

 assume a bacillary form afforded a valuable means of distin- 

 guishing it from S. pyogenes. 



II. MORPHOLOGICAL VARIATIONS DUE TO ENVIRONMENT. 



1. These maybe associated with differences in geographi- 

 cal distribution. For example, Schultz (1909) found that in 

 Cleveland, U.S.A., during the twelve months covered by the 

 investigation, "barred" forms of the diphtheria bacillus had 

 almost disappeared; during the same period in Boston and 

 Providence another observer noted that "barred" forms were 

 unusually common while "granular" forms were very rarely 

 met with. 



2. Prolonged cultivation may influence morphology. 

 Mohler and Washburn (1906) found that bovine tubercle 

 bacilli after 11 years' cultivation had become changed into the 

 human type. 



3. The crowding together of colonies on the surface of the 

 medium also influences morphology. In cultures of B. diph- 

 theriae, under these conditions, the change from the "solid" to 

 the "granular" type takes place much earlier than usual 

 (Denny, 1903). 



4. Changes in the medium employed may lead to changes 

 in morphology. Gordon (1900-1) published photographs 

 showing that the streptococcus associated by Klein and him- 

 self with scarlet fever may form, on serum, rods which closely 

 resemble the diphtheria bacillus, though in a liquid medium 

 it grows in typical streptococcal form. This fact may afford an 

 explanation of the observations, recorded by Duncan Forbes 

 (1903) and others, as to the prevalence of B. diphtheriae in 

 the ear discharges of patients suffering from scarlet fever, 

 without giving rise to symptoms of diphtheria and uninfluenced 

 by antitoxin. 



Ohlmacher (1902) and other observers have called attention 

 to the fact that streptococci from the throat in cases of 

 tonsilitis may, on Loeffler's serum, assume the form of bacilli 

 closely simulating B. diphtheriae. 



