296 W. C. ALLEE 



III. RHEOTACTIC RESPONSE UNDER EXPERIMENTAL CONDITIONS 



1. STREAM ASELLI 



a. With decreased oxygen 



The methods of handhng the problem of confining the isopods 

 in water having a low oxygen content, have varied more in the 

 progress of this work than those in any other line. The first 

 method tried was to keep the animals in an aquarium having no 

 inflow of water and containing a large amount of dead leaves and 

 other organic matter, which would absorb oxygen. This worked 

 after a scum had appeared to hinder the absorption of oxygen 

 from the air. Obviously, this method at best was crude, and 

 after trying boiling and cooling water in ordinary vessels, which 

 was of course very laborious, a machine for deaerating water was 

 devised. This apparatus was devised and built by V. E. Shelf ord 

 and the writer and will be described in detail elsewhere. In 

 brief, it consists of a tower down which the water runs through 

 successive sieves and is thus reduced to air saturation at the 

 temperature used. Then the water is heated in aluminum pans 

 over powerful gas flames until it is about to the boiling, point. 

 It is then cooled by passing through coils of block tin pipe sur- 

 rounded by tap water. In this way 1200 cc. of water can be 

 treated each minute and the oxygen content reduced from 8 cc. 

 per liter of water to less than half a cubic centimeter. By ar- 

 ranging the flow in the cooler any desired temperature can be 

 obtained. A gas introducer permits the addition of oxygen or 

 carbon dioxide to the deaerated water. 



Since the completion of this device the best results with low 

 oxygen have been obtained and most of the data to be given on 

 this subject are from work done with water prepared in this way. 

 I'he most important chemical changes due to the boiling, as shown 

 in analyses by Mariner and Hoskins of Chicago, are seen in 

 table 9.2 



In this work the animals to be used were first tested and then 

 placed in glass jars with ground glass edges. A glass plate was 



2 The complete table will be published later. 



