Researches on Nitrijying Bacteria 417 



until use in sterilized flasks in tlie refrigerator. The cores have 

 the obvious advantage of permitting us to compare several hori- 

 zons of the sediments collected. 



Physico-Chemical Study 



The two types of sediments are quite different from each 

 other, from a biological point of view. The temporary dry periods 

 and the vegetative covering of "Mattes" set them apart from the 

 muds of the bay, which belong to the true marine ooze type. One 

 has to stress, however, that the last type of sediment is never 

 very deep (with the exception of three samples) and the influ- 

 ence of land should not be overlooked. The physico-chemical 

 analysis of these two formations also differentiates them quite 

 clearly. 



The grain size composition of the two formations is extreme- 

 ly different. The muds of the bay are classified as a clay type. The 

 average content of bay clay is 60 per cent, whereas the basin 

 is only 13 per cent clay and a sand content of about 79 per cent. 



The pH is slightly different in the muds of the bay (7.3) and 

 the sands (6.9). 



The average carbonate content of muds is of 1.05 per 100 

 gm of dried mud, and 1.11 per cent of dry sand. Nitrogen con- 

 tent is quite similar to the two formations; 0.11 gm per cent in 

 the muds, 0.07 per cent in the sands. 



Comparative studies made at different depths of the same 

 sediment samples have not shown a relationship between the 

 nitrogen and carbon content and the vertical distribution. 



The phosphorus and potassium content of the specimens are 

 quite variable, but a relationship clearly exists between these 

 values and the depth or geographical location of the station. 

 Potassium varies between 70 and 110 mg per 100 g(dry weight). 

 We have also observed abnormally low concentration to 20 mg 

 per cent. The concentration of phosphorus fluctuates from a 

 trace to 60 mg per 100 gm diy weight. 



ANALYSIS OF THE RESULTS 



We will not give a detailed analysis of our results, but will 

 present the types of curves obtained when 20 gm of sediment 



