484 STUDIES IN IMMUNITY. 



growth of organisms thickens, and in 2 or 3 days projects dis- 

 tinctly from the surface. But although it becomes thicker it does 

 not broaden, so that its sides are distinctly steep. The influenza 

 bacillus, when grown in the same way, gives a much wider streak, 

 has a festooned outline which slopes gently, and is moist and 

 glistening. The whooping-cough growth, moreover, is whiter and 

 never blackens the underlying blood medium, whereas the influ- 

 enza bacillus frequently does so.* When the whooping-cough 

 bacillus is looked at with transmitted light the growth of organ- 

 isms appears as a pale line which stands out from the adjacent 

 part of the culture medium which has not been touched by the 

 inoculation. This clarification of the medium is due to the fact 

 that the organisms have hemolyzed the adjacent corpuscles and 

 so diminished the opacity of the nutrient substratum. 



We have already insisted on the fact that the abnormal forms 

 which occur frequently with the influenza bacillus in the form of 

 clubs or long filaments with a tendency of swelling, with irregularity 

 of aspect and poor staining, are rare in the whooping-cough bacil- 

 lus, which keeps its appearance of a small cocco-bacillus invariably. 

 The size of this cocco-bacillus, particularly in old cultures, may 

 be extremely reduced. We are speaking now of cultures on a 

 solid medium; the cultures on liquid media, which we shall 

 discuss in a few words, show more distinct pleomorphism ; the 

 dimensions of the organisms become more variable, their staining 

 more unequal, and they are frequently larger and less ovoid in 

 shape. 



Liquid cultures grow well, provided we take into account the 

 necessity of atmospheric contact, which is very marked in the 

 whooping-cough bacillus. We find, indeed, that the organism grows 

 only under the best conditions of aerobiosis. When grown in a 

 test tube containing a suitable nutrient fluid of several centi- 

 meters in depth, and maintained in a vertical position, the growth 

 of the organism is slow and difficult. When the tube is placed 

 horizontally, however, a cloud soon appears, covering the increased 



* These influenza organisms are obtained from cases of whooping-cough and 

 agree absolutely in all their characters with the organisms described by many 

 of our predecessors and notably by Jochmann and Krause. We may recall that 

 for a long time our attention was attracted by these organisms, which are con- 

 stantly present in the sputum of whooping-cough. 



