11 



100 Gr. water 

 10 „ peptone (Witte) 

 10 „ glucose 



4 „ citric acid 



0.4 „ MgSO^ 



1 „ Kil, PO, 



1 , NH^m, 

 The liqiiid from a pressed sponge (for culture-medium) was 

 übtained in this way : The superfluous water was pressed out of 

 some green sponges ; then the sponges were rubbed and the re- 

 maining liquid was filtered through a cloth, in order to separate 

 it from the intact sponge-cells (but not from the chlorophyll cor- 

 puscles etc). It was my intention to obtain in tliis way a me- 

 dium (without the living sponge) for the chlorophyll corpuscles, 

 differing as little as possible as to composition and concentration 

 from that in the living sponge. When this medium had to be 

 renewed, I could not make use again of pressed juice of a green 

 sponge — for the chlorophyll corpuscles cannot be held, not even 

 by filtering paper — ; I then used the juice of a colourless 

 sponge. 



In all these cultures appeared among a colourless, granular 

 ground-substance formed by sponge-rests, besides a great many 

 chlorophyll corpuscles, of course also some other organisms (algae, 

 protozoa, bacteria); so they were not pure cultures. To this fact 

 I owe many interesting data concerning the influence of such 

 organisms on a culture of my chlorophyll corpuscles. 



Nevertheless, I have tried in several ways to get really pure 

 cultures ; but always in vain. In the first place in the way in- 

 dicated by Beijekinck (4) for algae in general, the so called ge- 

 latine-method. As I did not succeed in applying this method to 

 the chlorophyll corpuscles — as little as Beijekinck — I will only 

 mention it in short: Before little colonies of the green chloro- 

 phyll corpuscles could be detected, the gelatine was always en- 

 tirely liquefied. I tried to suppress the development of bacteria 

 and mould in the originally sterile, neutrally reacting gelatine 

 by adding citric acid or sugar to it and by infecting with traces 



