104 • 



beginning of modern virus research — and, finally, in his studies on 

 the formation of indigo, and on the formation of glucosides in species 

 of Spirea. 



Meanwhile, however, the investigations started at the yeast 

 factory were continued, as appears from the papers on various yeast 

 species, on the pure culture of green algae and on the relation of 

 anaerobic organisms to f ree oxygen. 



An important contribution to general bacteriology was the more or 

 less systematic study on the acetic acid bacteria, which is based 

 largely on the experimental work performed by Beijerinck's col- 

 laborator D. P. HoYER, who in his doctorate thesis dealt with the 

 subject in more detail. 



However, it was only in the period between 1900 and 1910 that 

 Beijerinck's genius as a microbiologist came to full maturity. 



Almost imperceptibly, a principle came to the fore which will 

 remain for ever one of the foundation stones of microbiological scien- 

 ce, i.e., the principle of the accumulation experiment. Whilst until 

 then, the microbiologist who wished to study some special microbe 

 had to rely on his experience regarding the natural occurrence of 

 micro-organisms, and very often also was dependent on mere chance, 

 Beijerinck gave a convincing demonstration that in a great many 

 cases it was possible to find the desired germs in nearly every natural 

 material. It is true that as a rule the number of the particular germs 

 in any chosen material will be almost negligibly small so that direct 

 observation or isolation is quite impossible. However, Beijerinck 

 was the first to apply consistently the logical idea that by bringing 

 the material in question into a medium, the chemical composition of 

 which was specially adapted to the nutritional requirements of the 

 organism in question, an accumulation must occur which will make 

 subsequent isolation with the aid of the usual pure culture methods an 

 easy task. 



When we raise the question at what time this idea has first entered 

 the mind of Beijerinck, we have probably to go back to 1894. 



The first place in Beijerinck's publications where we were able to 

 tracé the use of the word "accumulation" ("Anhaufung") is in his 

 paper on sulphatereduction. The discovery and isolation of Spirillum 

 desulfuricans were a direct outcome of the application of the said 

 principle i). In several later investigations, too, the accumulation 

 principle was more or less consciously applied, yet it was not until 

 1 901 , in which year the paper on the urea bacteria was published, that 

 Beijerinck insisted on the great significance of the principle. In a 

 footnote the noteworthy remark was made, that its importance 



>) It must be remarked, however, that the first instance of a conscious application 

 of the accumulation principle is to be found in the fundamental investigations of 

 WiNOGRADSKY on the nitrifying organisms (1890). In his paper on Sp. desulju.icans 

 Beijerinck points out the analogy in procedure in the two cases. 



