744 THE AMERICAN NATURALIST. [VOL XXXII. 
(c) By enclosing the revolving receptacles in a circular 
chamber, thus lessening the resistance of the air. 
(4) When power was used, more satisfactory results were 
obtained by arranging the driving pulley so as to cut out the 
two largest sets of gears. Friction was thereby greatly 
reduced, and the necessary speed was gained from more rapid 
revolution of the driving pulley. 
(5) It is probable that four receptacles would work more 
satisfactorily than two. 
Some difficulty was experienced in avoiding leaks at the 
ends of the glass tube, At the distal end the insertion of a 
closely fitting, vaselined rubber “ mushroom ” (such as is used 
when repairing punctures in bicycle tires) was found to answer. 
Care had to be exercised to keep the entrance to the tube free 
at the proximal end. To obviate this difficulty it is hoped that 
a small, heavy annealed glass cone with a ground glass stopper 
at the apex can be devised in place of the tube. 
That the centrifugal method is beyond question the best 
method of collecting the substances suspended in the water for 
accurate determination seems to be proved, and great credit is 
due to Dr. Dolley for his demonstration of the fact. 
This method is. of value, not alone to him who wishes to 
determine the proportions of organic matter in drinking water, 
and to ascertain the quantity of microscopic plants and animals 
in water from special localities (a very accurate index of its 
commercial value for fish and shellfish cultivation), but it will 
enable biologists to study more successfully those lowly forms 
which lie close to the basis of life, the delicacy of whose struc- 
ture precludes handling by nets or filters. 
It is believed that the perfecting of the centrifugal method 
for collecting the Plankton will greatly facilitate the practical 
solution of the increasingly important question of the food 
supply for man, by ameliorating some of the difficulties which 
surround the rearing of edible fish in confinement. The eggs 
can be hatched by millions, but difficulty arises in obtaining 4 
natural or proper food supply. Hence in the case of most 
species the fry must be liberated very soon after hatching. 
But every additional day in which they can be kept in confine- 
