79 



an important degTee, the method was defective in that a small portion of the 

 catch, varying with the amount and chai'aeter of the plankton, remained on 

 the tilter paper, entangled in the fibers of its surface. To obviate this diffi- 

 culty and to secure, if possible, a method which would be effective and permit 

 the handling of a large quantity of water, experiments were made with the 

 centrifuge. The small machine described in the last report and adopted 

 by ns for nse in the measurement of plankton collections was found to 

 precipitate a large per cent of the organisms present in the water, accord- 

 ingly a larger machine was devised and built at the mechanical shops of 

 the University for this purpose It consisted of a hollow cylinder axis of 

 gun-metal with two returning arras, each bearing at the elbow a de- 

 tachable receptacle which receives flie solid rnatter precipitated from 

 the water, which last passed through the revolving axis and out to the 

 tips of the elbows before it returns to the axis for discharge at the lower end. 

 This machine is geared to give, with power, 8,000 revolutions per minute. 

 When fitted with cranks for two men, four to five thousand revolutions can 

 be obtained. This apparatus was tested with water from the river at a time 

 when it was full of water bloom, — -formed principally of Carteria, — and also 

 with water from the lakes in varying kinds and amounts of plankton. It 

 proved to be more effective in the removal of the plankton than any method 

 previously tried, but the operation of the machine by hand was extremely la- 

 borious, and the precipitation of the plankton was very slow. Furthermore, 

 a variable and oftentimes considerable amount of the plankton — especially 

 that found in the water-bloom — is at times lighter than the water, and thus 

 can not be removed by centrifugal force with the heavier constituents. 



In November, 1897, a Berkefeld army filter (system Bruckner), was added 

 to the plankton equipment. It is very efficient in removing all the solid mat- 

 ter from the water, and its operation with ordinary samples is quite rapid. It 

 consists of a force-pump and a cylinder of diatomaceous earth, upon which 

 the plankton and silt contained in the water ai'e collected. This is removed 

 by washing with a brush, but in the process a part of the substance of the 

 cylinder is bi-ushed off. This debris is added to the silt of the water and 

 renders subsequent microscopic examination more difficult. The brushing is 

 also disastrous to some of the more delicate organisms, but leaves by far the 

 greater part of the minute forms which escape the silt intact and in suitable 

 condition for enumeration. 



During the past two years some progress has been made with an examina- 

 tion, measurement, and enumeration of the plankton of the regular series, 

 though much of the time has been given to the preparation of plankton ap- 

 paratus and the improvement of the method. In this work the examination 

 of the the test collections by the enumeration method has been particularly 

 time-consuming. The work of enumeration has been facilitated by the use 

 of a set of six counting machines, which enable the observer to keep a record 

 of six different species at once without the mental effort of carrying the 

 count in the mind. An extended amount of this work remains to be done be- 

 fore we shall utilize to any considerable extent the collections now accumu- 

 lated. This work will be necessary to the full confirmation of the results of 

 our investigation, and will also be very valuable in suggesting new fields for 

 development, especially along experimental lines. The present provision for 

 this work is quite inadequate to a prompt return for our present investment 

 in this department of the operations of the station. The enumeration of the 

 smaller organisms, especially under the higher powers of the microscope, is 

 particularly taxing upon the eyes, and long continued application is a severe 

 strain upon the nerves of the plankton statistician. I believe it to be possible 

 by the expenditure of a small amount of money to secure student aid for 

 some of this work in such a way as to render promptly available a consid- 

 erable portion of the now latent results of our plankton work. 



The sanitary analyses of the water in connection with the chemical survey 

 of the waters of the State have been continued. Weekly samples have been 

 collected thi'ough the two years from the Illinois river and from Spoon river 

 on days when plankton examinations hive been made. Similar regular col- 

 lections were commenced in Thompson's and Quiver lakes in September and 

 October of 1897, and have been continued in connection with the fortnightlj' 



