69 



cation between the pair of elements. At any rate in the spe- 

 cimens I have had to deal with there has never been any 

 difficulty in deciding whether a pure culture consisted of Gram- 

 negative cocci or cocco-bacilli. (By a cocco-bacillus we do not 

 understand an intermediate form 1 between a coccus and a ba- 

 cillus (rod), but a coccus-like bacillus). One gets a decided 

 impression that there are no transitions between these two 

 forms, but rather a distinct gap. 



Yet Pfeiffer's bacillus, especially in sputum, but also in cul- 

 tures, may greatly resemble Gram-p o s i t i v e cocci (Pneumo- 

 coccus, „Diplostreptococcus") in shape. As Gram staining was 

 always used there was again no difficulty in distinguishing 

 it from these. 



(b). There are quite continuous transitions between 

 coccus-like forms and well-marked rod-forms. Furthermore, 

 there are often in the same preparation both quite short and 

 longer forms; and the sam'e strain can in different genera- 

 tions" now present itself markedly coccus-shaped, now m'arkedly 

 rod-shaped; finally different strains, of which one consists of 

 quite short elements, while the other appears in well-m'arked 

 rod-form, may be so quite similar in their other properties, that 

 it would be unreasonable to designate the first as a coccus and 

 the second as a rod. 



2. The appearance of the growth on blood- 

 agar. On this medium (i. e. peptone broth agar with 

 a content of 20— 25% fresh defibrinated unheated horse blood), 

 Pfeiffer's bacillus grows in pure culture as translucent flattened 

 colonies, only a fraction of a mm' across. The culture often 

 idevelops a darker colouration of the blood-agar in the im- 

 mediate neighbourhood, but never haemolysis. 



3. The appearance of the growth on haemo- 

 pjlobin-agar, that is to say agar with the addition of one 

 of the soluble blood derivatives which have proved favourable 

 for the growth of Pfeiffer's bacillus (haemolysed blood; pepsin- 

 digested blood). The growth on these is far more luxurious 

 than on blood-agar. With scanty inoculation, semi-translucent, 

 usually rather flat colonies of 1—3 mm', diameter make their 

 appearance. The centre of the colony is as a rule, — but not 

 always. — darker than the periphery and forms a little eleva- 



