SECONDARY INFECTIONS 509 



4. Agglutination. 



Pfeiffer's bacillus is not specifically agglutinated by the serum of patients 

 suffering from influenza and in whose sputum the organism is present 

 (Meunier). 1 



The serum of immunized animals agglutinates the bacillus in dilutions of 

 1 in 200 to 1 in 500 (Cantani). 



5. Secondary infections Ancillary micro-organisms. 



In persons suffering from influenza certain micro-organisms are able to 

 develop side by side with Pfeiffer's bacillus 2 and produce complications 

 of the original disease. The micro-organisms commonly found associated 

 with Pfeiffer's bacillus are streptococci., pneumococci, staphylococci and bacillus 

 coli. These micro-organisms appear to favour the development of Pfeiffer's 

 bacillus and to facilitate its growth. 



Grassberger has pointed out that in artificial cultures, in presence of the 

 staphylococcus aureus, the colonies of Pfeiffer's bacillus grow to an unusually 

 large size so that they become visible to the naked eye in 24 hours. 



The colonies remain transparent, and nearly colourless or bluish, the centres being 

 sometimes greyish in colour : they are almost confluent but their margins do not 

 blend. These giant " influenza " colonies are seen lying in the hollows between the 

 larger staphylococcal colonies : sub-cultivated alone on blood-agar (without the 

 staphylococci) they give rise to colonies of normal appearance which retain their 

 vitality longer than usual. 



Pfeiffer's bacillus is less sensitive also to the reaction of the culture medium when 

 grown symbiotically with the staphylococcus, so that it will then grow on quite 

 markedly alkaline blood-agar. 



The various staphylococci, and in a lesser degree the colon bacillus, the 

 typhoid bacillus, the diphtheria bacillus, and streptococci all exhibit this 

 ancillary influence. 



The influence of these organisms on Pfeiffer's bacillus seems to depend upon the 

 action of certain substances secreted by them or to some change induced in the 

 medium as a result of their growth. Thus, if a 24-hour agar culture of a staphy- 

 lococcus be sterilized in the autoclave, poured into a Petri dish, and sown with 

 Pfeiffer's bacillus after smearing the surface with blood, the organism will grow 

 in the form of the large colonies referred to above (Rosenthal). 



This fact can be easily demonstrated in the following manner : Sow a 

 culture of Pfeiffer's bacillus all over the surface of a blood-agar medium and 

 after incubating for 3 or 4 hours at 37 C. to evaporate the excess -of moisture 

 and to get rid of bubbles, sow a narrow stroke culture of the staphylococcus 

 on the surface or make two or three punctiform stabs. On incubation at 

 37 C. Pfeiffer's bacillus will form giant colonies like satellites around the 

 staphylococcal colonies. 3 



Rosenthal suggests that this ancillary action of the staphylococcus might 

 be applied in cases where search for Pfeiffer's bacillus has yielded doubtful 

 results : thus if tubes sown with sputum or blood remain sterile after incubat- 

 ing for 24 hours, he suggests that a staphylococcus might be sown in a 

 narrow streak on the culture medium in the hope that it might stimulate 

 the latent bacillus. 



1 It must be remembered that normal human serum and the serum of normal animals 

 will agglutinate Pfeiffer's bacillus in dilutions of 1 in 10 to 1 in 20. 



2 In 6 only out of 30 cases of influenza studied by Grassberger was Pfeiffer's bacillus 

 found in pure culture. 



3 The Micrococcus prodigiosus has a similar effect, but the cultures of this coccus must 

 be sterilized by heating for 20 minutes at 60 C., since sterilization in the autoclave destroys 

 the action (Luerssen). 



