CH. Il] BLOOD METHOD. 39 



Press the plants down into the water with an inverted 

 funnel, w^hich should be a large one, and should fit easily 

 inside the jar; its neck should be cut short, so that the 

 opening may be easily submerged. The gas given off by 

 the plants will be guided by the funnel and may be 

 collected in an inverted test-tube filled with water and 

 placed over the opening. If the neck of the funnel is 

 covered with one or two centimeters of india-rubber 

 tubing, and if a test-tube be selected which fits tightly 

 over the tube, no other support for the test-tube is 

 needed. The funnel may be kept in its place by 3 bent 

 glass rods attached to its neck and hooked over the rim 

 of the jar. 



When the test-tube is nearly full, the gas may be 

 shown to be oxygen by the glowing of a splinter of deal 

 which has been lighted, and is blown out just before it is 

 thrust into the gas. The test-tube should be of such a 

 size that it can be easily covered with the thumb. 



(48) Engelmanns blood method^. 



A flask containing defibrinated bullock's blood is 

 attached to the water air-pump and exhausted of oxygen. 

 The fluid appears to boil during the process, which is 

 assisted by the application of a temperature of about 

 35° C. The blood may be preserved in a venous con- 

 dition, and may at the same time be charged with the 

 necessary COo by being tightly corked with a supply of 

 carbonic acid. 



Engelmann recommends a filament of Spirogyra about 



^ Pfluger's Archiv, Vol. xlii. 



