212 



The others were on the whole ovoid, sometimes oblong and 

 sometimes almost spherical. In a number of the cultures 

 scanty thread-shaped elements were observed, of moderate 

 length and usually rather thick, and also transitions between 

 these and chains of the ordinary ovoid bacilli. Sometimes 

 ovoid elements of unusual size were seen. Marked polar 

 staining was only exceptionally observed. On the whole 

 however these strains as well as several hundreds of other 

 strains of the whooping-cough bacillus have shown that the 

 morphology of this organism is far more uniform 1 than that of 

 Pfeiffer's bacillus. The ovoid form is very characteristic of 

 the whooping-cough bacillus, but given an individual prepa- 

 ration one cannot be certain from the microscopic appearance 

 alone whether one has a whooping-cough bacillus or a Pfeif- 

 fer's bacillus to deal with. 



On inoculation on ordinary agar none of the strains 

 gave the slightest growth. 



On haemoglobin agar only the 3 oldest strains grew, 

 but the growth gradually became rather good. Some strains 

 were tested for growth on Fildes agar with negative results. 

 The oldest strains grew on Levinthal agar (November 1921) 

 but the younger one did not, even after repeated attempts. On 

 „chocolate" agar both the young and old strains grew though 

 not so well as on blood agar. Pfeiffer's bacillus which was 

 inoculated at the same time as the whooping-cough bacillus 

 on the four last-named media, grew excellently. 



That it was the oldest strains that grew on haemoglobin 

 agar was no mere chance. It is a known fact that the whooping- 

 cough bacillus can be trained to grow on ordinary agar (Bordet 

 & Sleeswyk and others), and that on the whole it becomes 

 less „fastidious" after a long period of cultivation. Thus I 

 have observed that by subculturing daily for a long time the 

 cultures acquire a considerably increased energy of growth. 

 The reason these facts are not very prominent in the present 

 material, is undoubtedly due to the fact that the strains have 

 only been subcultured with a 3 — 4 Week's interval and after 

 incubation they were kept in the cold room. The power of 

 adaptation is a property that always distinguishes the 

 whooping-cough bacillus from Pfeiffer's bacillus which pre- 

 serves its growth energy and its dependence on haemoglobin 



