Immediately after the „Spanish illness" had arrived in Den- 

 mark in the beginning of July 1918, an investigation was 

 set on foot at the State Serum Institute into the bacteriology 

 of the disease. 



As a collaborator in this work I succeeded in demonstra- 

 ting Pfeiffer's „Influenza Bacillus" , few days after the be- 

 ginning of the investigation in 5 of the patients from whom 

 samples were taken. This finding directed the bacteriological 

 investigations, which were undertaken under the direction of 

 the Chief of the Department at that time, Dr. Oluf Thomsen, 

 to a large extent towards demonstrating Pfeiffer's bacillus in 

 influenza and other diseases, as well as in healthy people. 



I continued these investigations in the following years, for 

 the first few months in collaboration with Dr. Thomsen and 

 afterwards independently. The original object was only to 

 obtain as comprehensive an idea as possible of the occur- 

 rence of the bacillus here in Denmark in the various phases 

 of the pandemic and after it had ceased. But another que- 

 stion soon claimed my attention to a greater extent. It ap- 

 peared that while the colonies of Pfeiffer's bacillus from in- 

 fluenza patients were always of very characteristic appearance 

 in cultures and easy to distinguish from colonies of other 

 species of bacteria and the microscopic picture did not usually 

 display great differences, the conditions were more complex 

 in the case of samples from healthy persons as colonies of 

 haemoglobinophilic bacteria could vary considerably more, both 

 in macroscopic and in microscopic appearance, making it dif- 

 ficult to judge where the boundary between Pfeiffer's bacillus 

 and other bacteria ought to be placed. 



