On the Precipitation of Calcium Carbonate. 21 



Under expeditionary conditions, and in the absence of the somewhat 

 elaborate apparatus that would be necessary in order to estimate chemically 

 the amount of denitrification in cultures, it was only possible to compare the 

 rate of denitrification in different cultures by noting the time taken for the 

 first appearance of the nitrite reaction and the time taken for all trace 

 of nitrite or nitrate to disappear. It seems that the rate of denitrification 

 in culture media inoculated with equal volumes of samples of sea-water 

 must be a function of the number of bacteria in the sample, the temperature 

 at which the cultures are grown, and the specific power of denitrification of 

 the individual species of bacteria. Considering the rapid multiplication of 

 bacteria when the food supply is plentiful, up to a maximum determined 

 chiefly by the accumulation of the waste products of their own metabolism, 

 it appears that the factor of the number of bacteria in the sample may be 

 neglected within the limits of these experiments. For example, the number 

 of bacteria in 1,000 c.c. of Gran's medium at the end of 24 hours would 

 probably be much the same whether it were inoculated from a sample con- 

 taining 8 or 16 bacteria per i c.c; similarly it was a matter of experience 

 that the first trace of nitrite formation was observable at about the same 

 time, whether 5 or 10 c.c. of a given sample had been used for inoculation. 



Consequently It would appear that for purposes of comparison, and 

 within the limits of the experiments described, if the temperature be the 

 same for the cultures compared, the rate of denitrification is a measure of 

 the specific denitrifying power of the particular species of bacteria. 



In the work on the bacterial precipitation of calcium carbonate, the 

 precipitate (which was often so fine as to tend to remain in suspension) 

 was usually obtained by centrifuglng. It was either preserved in small 

 bottles with some of the culture fluid, or else washed first with distilled water 

 and then with absolute alcohol, and finally allowed to dry. These precipi- 

 tates were sent to Dr. F, E. Wright, of the Geophysical Laboratory of the 

 Carnegie Institution of Washington, who with great kindness reported 

 on their mineralogical properties. 



INVESTIGATION OF SAMPLES OF SEA-WATER TAKEN OFF PORT ROYAL. 



JAMAICA. 



The work at Port Royal was done in May 191 1, but was of a very pre- 

 liminary nature. It was necessary to depend on a sailing-boat for obtaining 

 the samples; yet, owing to the remarkable regularity with which an on-shore 

 wind springs up every morning, but little difficulty was experienced from this 

 cause. No apparatus for obtaining deep samples was available, but samples 

 were taken from a depth of 6 fathoms by means of a bottle from which the 

 stopper was pulled by a line and then allowed to fall back Into place. A 

 measurement of the rate of denitrification in fluid culture media inoculated 

 with samples of sea-water was made, but Isolation of the bacteria on solid 

 media was not attempted. The following method was employed: 



