THE ESSEX FIELD CLUB. 
239 
lecting bottle without the intervention of a net or other filtering appliance, 
and without any preservative being added, as it was most important 
that the organisms obtained should be examined alive. For a similar 
reason the sample should be centrifuged as soon as possible after col¬ 
lection. Very small quantities of water sufficed as a rule to give a fair 
idea of the nannoplankton organisms present and their relative abundance. 
The glass tubes commonly supplied with a small centrifuge holding about 
15 cc., were ample for most fresh-water investigations, and Mr. Scourfield 
exhibited a modification of a “ haematocrit " head for the centrifuge 
which he had had made to carry elongated vase-shaped tubes, holding 
only 1 1 cc. These, he said, usually gave good results for small pieces of 
water such as ponds, but would scarcely be sulficient for the examination 
of large lakes in which the organisms were as a rule not so relatively 
abundant. After the actual centrifuging for a minute or two at speeds 
ranging up to as much as 10,000 revolutions per minute with the “ hae¬ 
matocrit ” head (two separate centrifugings being recommended for each 
sample, one at a comparatively low speed and one at the highest speed 
obtainable), all the water except a minute drop at the bottom should 
be pipetted off with a fine “ Rousselet ” pipette. This drop should be 
sucked up and expelled a few times with the pipette in order to detach 
any organisms adhering to the bottom of the tube and then a portion 
or the whole of it transferred to a glass slip, live-box or compressor and 
placed under the microscope for examination by the usual methods. 
The tiny organisms so obtained were found to belong mainly to the 
groups of the Bacteria, Schizophvceae, Desmids, Diatoms and Chlorophyceae 
among the plants and Heliozoa and Flagellata among the animals. They 
ranged in size from about 1-1000" downwards to the smallest Bacteria, 
and, strangely enough, very few, if any, seemed to suffer from the centri¬ 
fuging process. Their very minuteness and close approximation to 
the specific gravity of water was no doubt a protection to them against 
the centrifugal pressure. Many of the forms appeared to be undescribed, 
but it was difficult to say at present how far this was really the case. Some 
were certainly new to science, and one which had been obtained from a 
pond on Leyton Flats had recently been recorded byJProf. G. S. West, as a 
new species and type of a new genus. .j,. 
The proof of the great abundance of these very minute forms in most 
waters had come almost as a revelation, and had led to an increased 
appreciation of the important role played by living organisms in ponds 
and lakes and also in the sea. The significance of the nannoplankton 
as a source of food for many Fntomostraca, Rotifera, &c., and thus in¬ 
directly for the still higher and larger aquatic creatures, had been amply 
demonstrated. And thus, as was indeed usually the case, a new method 
of investigation was found to lead to an altogether wider outlook upon 
matters about which all essential facts were supposed to be well known. 
Lime-stone Deposit of the River Can. —Mr. Percy Thompson ex¬ 
hibited specimens of an impure limestone deposit formed by the small 
river Can, to the northwest of Chelmsford. 
The deposit occurs in the bed of the river in various places from above 
Pengymill down to the Chelmsford-Roxwell road near the point where 
it is joined by the Roxwell Brook, a distance of about ii miles, and forms 
