14 



On the otlwr liaiul, the variety- of uses whifh must now be "nia<le of pre- 

 jServefl material in the course of o\ir Station studies necessitates the frequent 

 .employment of the nicest methods of the histological laboratorj-, and a com- 

 plete acquaintance, at least, with laboratoi-y methods in general. 



Definite and precise comparisons of different aquatic localities with respect 

 to their biology have first been made possible in some considerable measuiv 

 by the comparatively recent introduction of more or less exact quantitative 

 methods for the collection and determination of the biological contents of the 

 water. These, commonly known as plankton methods, enable us also to 

 study the biologfcal history of any locality to which they are fully applicable, 

 by making it possible to bring into close comparison the organic contents of 

 the water from day to day, fi-mn season to season, and from year to year. 

 Unfortunately, these methods are not as yet capable of application to all 

 aquatic forms in all situations, l)ut have been used successfully" only for the 

 smaller plant and animal forms of the clear open water. 



By using always identical apparatus in a perfectly uniform manner for the 

 accumulation of microscopic and semi-microscopic objects in such waters 

 and preserving the product by identical methods, it is possible to make and 

 keep collections which may serve as a means to a precise comparison of the 

 mass of organic life in the waters studied, or of the uTimber of individuals 

 representing any selected species. 



In our own Station work these plankton operations have been carried 

 forward from the beginning at all the substations where open water could l>e 

 found in condition to permit the hauling of our plankton net, or, later, the 

 use of the plankton pump. A large number of qitantitative determinations 

 of collections so made have been worked out in a way to give the actual 

 quantity of organic life in a cubic meter of water for each situation studied 

 by this method, and enumerations of various forms have likewise been made 

 under the microscope by methods such as to give us reliable data for a com- 

 parison of the various waters with reference to the ntimber of such forms in 

 a cubic meter of water. Approximately quantitative collections have like- 

 wise been made, wherever possible, in situations which do not permit the 

 tise of this plankton apparatus, but with results far less reliable, of course, 

 because based mainly on personal estimates, and made Viv the use of . less 

 precise and exhaustive methods. 



It seems not impossible that (juantitative and numerical plankton work will 

 be found to have a certain value as a ground of infei-ence concerning the 

 biological contents of water Avhich cannot be searched by the plankton appa- 

 ratus. In other words, definite, if general, relationships may be found to 

 exist between the amount and composition of the plankton in the free and 

 open water of a given lake or stream at any given time and the mass and 

 variety of livitig forms contained in the marginal shallows or imbedded in 

 the mud of the bottom. ■ 



Considi'rable modifications have been made at the Station since it opened, 

 in the details of the (juantitative method, often forced upon us by the pecu- 

 liarities of the location and the special conditions under which our work was 



