Ill 



which the name of aerophilous organisms was given seek the 

 highest oxygen tension in the preparation, the organisms of the 

 second, microaerophilous, group evidently prefer lower oxygen ten- 

 sions. The growth of several so-called obligately anaerobic bacteria 

 was watched both in cultures under the microscope and in shake 

 cultures. In all cases it was observed that optimal proliferation oc- 

 curred at those spots where low oxygen tensions prevailed. At the end 

 of his paper BEIJERINCK stated explicitly that he did not offer 

 experimental proof for his belief that all living organisms known at 

 that time require free oxygen for their existence. Indeed, the ex- 

 periments reported demonstrate only that use is made of oxygen in 

 so far as this gas is accessible, and it is admitted that obligately 

 anaerobic bacteria can produce thousands of generations without a 

 renewed contact with free oxygen. 



Yet for some facultatively anaerobic bacteria like B. coli oxygen - 

 in surprisingly small quantities - - is indispensable for the maintenan- 

 ce of life. No explanation could then be offered for this singular fact, 

 and it has not been elucidated in later years. 



c. Studies on luminous bacteria. 



The existence of bacteria capable of emitting light having been 

 demonstrated by PFLUGER in 1875, some years elapsed before other 

 investigators made a closer study of the various species showing this 

 remarkable property. 



In June 1887 FORSTER, who was professor of hygiene at the Uni- 

 versity of Amsterdam, reported at the meeting of the "Koninklijke 

 Akademie van Wetenschappen" at Amsterdam ! ) the outcome of some 

 investigations on the properties of luminous bacteria, and shortly after- 

 wards his assistant TILANUS also published a paper on the subject 2 ). 



It seems probable that these publications contributed to the fact 

 that in the next year the industrial microbiologist BEIJERINCK also 

 gave his attention to the group in question. The first entry in his 

 laboratory note-book dealing with luminous bacteria is dated Janu- 

 ary 12nd, 1888; on that day a sample of luminescent pork received 

 from a Mr. ENKLAAR at Deventer was submitted to a bacteriological 

 analysis. A little later BEIJERINCK seems to have entered into contact 

 with Professor B. FISCHER of Kiel, who had already described several 

 species of luminous bacteria, and the second half of 1 888 was mainly 

 devoted to a comparative study of FISCHER'S strains and those isola- 

 ted by BEIJERINCK himself. 



As a result BEIJERINCK gave in 1889 a survey of the various species 

 of luminous bacteria then known. He also isolated from water of the 

 North Sea a new species, to which he give the name of Photobacterium 



1) J. FORSTER, Centralbl. f. Bakt. u. Parasitenk. 2, 337, 1887. 



2 ) C. B. TILANUS, Tijdschr. v. Geneesk. 2, 169, 1887. 



