114 



North Sea after hot days in the summer months i). Beijerinck 

 observed in this species the remarkable phenomenon of aggregation, 

 due to the micro-aerophily of the majority of the individual cells. He 

 also reported the interesting observation — made in collaboration 

 with F. C. Gerretsen — that luminous bacteria exposed to ultra- 

 violet radiation lose their reproductive function rather quickly, whilst 

 they continue to emit light for several hours2). This experiment 

 provided the first and so far the only example of light emission by 

 material derived from luminous bacteria, i.e., in the absence of nor- 

 mal cells capable of reproduction. In a final part, Beijerinck dis- 

 cussed many observations regarding the variability of Ph. splendidum 

 from the standpoint of the genetic views prevailing at that time. 



d. Pure cultures of algae, zoochlorellae, and gonidia of lichens. 



In Part II of this book due attention has already been given to the 

 fact that Beijerinck was the first to obtain pure cultures of algae, 

 zoochlorellae, and gonidia of lichens (Cf. Chapter XVI). Although for 

 this reason Beijerinck's activities in this field will not be surveyed 

 here, it seemed desirable to include at this spot this brief reference to 

 these studies which constitute one of the most important contributi- 

 ons ever made to the science of microbiology. 



e. Studies on yeasts. 



It is only natural that Beijerinck's industrial activities should 

 have brought him already at the very beginning of his microbiological 

 career to a detailed study of various yeasts. In the meantime the 

 industrial importance of many of his investigations in this field will 

 have prevented publication of their results. Notwithstanding this, 

 in the course of time, Beijerinck was able to publish several valuable 

 contributions to our knowledge of this group of micro-organisms. 



When Beijerinck commenced his researches, the study of yeasts 

 had been mainly restricted to those species and strains which found 

 technical application in breweries, distilleries and in vinification. Fol- 

 lowing the lead of E. Chr. Hansen, Beijerinck was one of the first 

 to realize that these cultivated species were merely adapted forms of a 

 large group of "wild yeasts" having a wide distribution in nature. 



In his study on kefir Beijerinck gave a description of the yeast 

 constantly present in this Caucasian product 3). The organism had 

 already been discovered by Kern in 1881, but Beijerinck added 

 several interesting details tq Kern's description. Especially note- 



1) Folia Microbiologica 4, 15, 1916. Ph. splendidum differs from the related Ph. lu- 

 minosum by its much higher temperature optimum. 



2) These experiments were later described in more detail by Dr. Gerretsen. Cf. 

 Centralbl. f. Bakt. u. Parasitenk. II, 52, 353, 1920. 



3) Arch. néerl. d. sciences exactes et naturelles 23, 428, 1889. 



