ADDITIONAL NOTE ON WHOOPING-COUGH BACILLUS. 483 



ditions are avoided, colonies may be obtained even in the first 

 culture, which, although not close together, show a good growth at 

 the end of the third day, and are distinguishable by their whiteness, 

 their projection and their clearly circumscribed outline. 



Certain sputa which are particularly favorable, when suitably 

 diluted and inoculated on the culture medium have given us almost 

 pure cultures, including 100 to 200 times as many whooping-cough 

 colonies as colonies of other bacteria. 



We have, as well as other authors, mentioned the frequency of 

 a bacterium similar to that described by Pfeiffer as the cause of in- 

 fluenza, in the sputum of whooping-cough,* and we have also men- 

 tioned the fact that the presence of these organisms offers a serious 

 obstacle to the isolation of the true parasite of whooping-cough. 

 They usually form numerous colonies which develop rapidly. These 

 organisms are not agglutinated by the serum of a horse immunized 

 against the whooping-cough bacillus, although this serum agglu- 

 tinates the latter organism energetically; the serum may therefore 

 be used as a ready and infallible means of differentiation. Micro- 

 scopically these organisms are frequently rather difficult to dis- 

 tinguish from the real whooping-cough organism. f A few suc- 

 cessive cultures on blood media suffice to distinguish the two 

 organisms with certainty. When the whooping-cough bacillus is 

 inoculated on the surface of blood agar in a delicate streak, the 



* We might better say, identical with, rather than similar to. We have culti- 

 vated for some time parallel cultures of bacteria of this sort coming from cases 

 of whooping-cough and the typical influenza bacillus which was kindly given us 

 by Dr. Cohen, who obtained it from Pfeiffer's laboratory. Comparison of these 

 cultures shows no perceptible difference between the organisms. 



f This is particularly true in the first generation of cultures. Certain indica- 

 tions on this point may be useful. On suspending in water to make a stained 

 preparation, the influenza bacilli give an emulsion with a tendency to spontaneous 

 agglutination, so that in drying on the slide they are often clumped in. small masses 

 (see, for example. Fig. 1, plate 9, in Jochmann and Krause's article, Zeitschrift 

 fur Hygiene, 1901); in preparations of whooping-cough the organisms are better 

 separated. After several successive cultures on our medium, the influenza 

 bacillus often assumes larger shapes, which are frequently swollen and twisted; 

 the mean size increases and is frequently greater than that of the whooping-cough 

 organism. Cabolated blue stains color the influenza bacillus much more intensely 

 than they do the whooping-cough organism. We may recall that transplanting 

 on ascites-agar serves as a good method for distinguishing the two organisms; the 

 whooping-cough bacillus grows on it slowly as a white streak; the influenza bacillus 

 grows very slightly, although it does grow somewhat. 



