14 Periodicity in Active Numbers of Soil Flagellates 



method employed is a dilution one, fully described in a recent paper (6). 

 Briefly, it consists of dividing the sample into two 10 gr. portions. 

 One of these is made up into a series of suitable dilutions, from each 

 of which 1 c.c. is inoculated on to agar plates which are incubated at 

 18° C, and examined at 7 and 14 day intervals. If, for example, growth 

 occurs in the 1/1000 dilution plates there was at least one organism 

 producing this growth, and it is assumed that there are at least 1000 per 

 gr. of soil. Thus by using dilutions sufficiently near to one another 

 the total number of protozoa per gr. of soil can be ascertained. To find 

 the number of active forms the second 10 gr. portion of the soil is treated 

 overnight with 2 per cent. HC1 ; this kills all active forms leaving the cysts 

 uninjured. The number of protozoa in this treated sample subtracted 

 from that in the untreated gives the number of active protozoa per gr. 

 of soil. Proof of the accuracy of this method is given in the paper re- 

 ferred to above, and further proofs are annexed on pp. 14 and 16 of the 



present paper. 



RESULTS OF DAILY COUNTS. 



The daily numbers of active and cystic forms of the three species of 

 flagellates are given in Table I and Figs. 3 and 4. It will be seen that 

 the total numbers — trophic and cystic — exhibit great fluctuations, rarely 

 being the same for two days together. The most remarkable feature 

 presented by the results, however, is the wholly unexpected daily 

 periodicity in the fluctuation in numbers of the trophic forms. We 

 think there is no doubt as to the reality of this periodicity. 



Table I. Giving the total — cystic and active — numbers per gr. of soil for 

 three species of flagellates on successive days, beginning February 9th 

 and ending March 8th, 1920. 



