— 9 — APPENDIX D: BRANDT 



1902 and 1903, they occurred very commonly, but in August 1904, more rarely than at any 

 period of year yet investigated. In general they seem — apart from this exceptional case 

 — to occur in greater abundance in August and February than in May and November. 

 All the samples of denitrifying bacteria, even those taken in February, thrive better in the 

 warmth than in the cold. The two groups of denitrifying bacteria act differently physiologi- 

 cally and their distribution is also different. The one group, reared in Baur's culture- 

 solution, occurs in general in greater quantities and more uniformly in the North Sea and 

 Baltic than the other group reared in Gran's culture-solution. Whilst the latter play 

 their part on and in the bottom-soil chiefly, less on the surface, and are but seldom 

 found in the middle layers, we may meet with Baur's denitrifying bacteria in almost all 

 layers of water and in the most varied bottom-samples. They occur almost always in the 

 surface-water of the North Sea and Baltic, and they are even more numerous in the 

 bottom-samples from the Baltic than Gran's bacteria, but decidedly less than these in 

 the bottom-samples from the North Sea. 



Though it appears from the general distribution of the denitrifying bacteria in the 

 home-waters, that they play an important role in the sea, and though it appears very 

 probable also, from the evidence regarding their better growth in warm water, that the 

 relative richness of the cooler seas is connected with the smaller disturbance of the 

 nitrates and nitrites, yet detailed investigation is wanted concerning the denitrifying bacteria 

 of the warm regions of the sea and the content of the tropical seas in regard to nitrates 

 and other nitrogen compounds. If such an investigation shows, contrary to expectation, 

 that the warm seas have just as great or even a greater content of nitrates than the 

 colder, then my hypothesis regarding the disturbing role of the denitrifying bacteria in the 

 tropical seas cannot be maintained. We should then require to give a new explanatory 

 hypothesis and investigate more closely. The other plant food-stuffs occurring but in 

 traces, e. g. calcium phosphate and silicic acid, would then come into consideration. The 

 termination of this further investigation will be gained most quickly by well-regulated 

 rearing experiments with separate culture-solutions. 



First of all, our endeavours must be directed to make the methods of receiving and investigation 

 preservation, and of the quantitative determination of the silicic and phosphoric acids, as a°jd'an/phos- 

 free of error as possible, and to determine for the home-waters the amount of these food- phaies.dis- 

 stuffs during the different periods of the year. ^°'^wat"r^^* 



Since the beginning of the quarterly cruises of the "Poseidon", water-samples have 

 been collected suitable for this purpose, and then examined in the laboratory by Dr. Raben 

 for their silicic and phosphoric acids. Up to the present, Dr. Raben has only reported on 

 the quantitative determination of the silicic acid dissolved in sea-water, based on values 

 obtained from 25 analyses during the year 1903. If we also lake into consideration the 

 silicic acid determinations of water-samples taken in August and November 1902 and in 

 February, May and August 1904, all made by Dr. Raben, we now have 61 quantitative 

 determinations, 27 for the North Sea and 34 for the Baltic. The average of ail these 

 determinations is 09 1 mgr. SiO^ per liter, for the Baltic alone 0'978, for the North Sea 

 0"84. I give below, the average of the 34 analyses of the open water of the Baltic, the 

 number of the various samples examined being given in brackets. 



Appendix D 2 



