RESPIRATORY DIFFERENCES. 



381 



D 



The apparatus which I have Been using has the following 

 simple construction, illustrated in the accompanying figure. It 

 consists of a Pyrex test tube A, without rim, 100 mm. long by 

 10-12 mm. diameter, capacity about 10 cc. This is 

 surmounted by a piece of rubber tubing B, into 

 which fits a short length (about 40 mm.) of Pyrex 

 lulling C of the same diameter as the tube A. Over 







tin- end nf (' i- .mother piece of rubber tubing D. 

 The rubber nibin^ must fit tightly over the glass and 

 if necessary /' < an be wired to .-1 and D to C, but 

 mil ( t.i Ji. A number of such outfits should be 

 prepared. I or the water blanks only the parts A 

 and B are nei e-sary. 



The app.iraMi- is used as follows. In those tubes 

 which ate to contain the animals all four pieces 

 nm-t be titled together as in the figure and C' must 

 be sho\e<l dose to but not in contact with .1. All 

 of the tube- to be used in one experiment, including 

 the tube- tor the blanks, are filled by siphon with the 

 -aim u.i i ei I' loin an elevated receptacle. Tlie -iphou 

 should reach to the bottom of the tube and tin- \\ ater 

 illo\\cd to How out of the top for some time. 

 '1 I" animal- to be used can be placed in the tube- 

 : hey are tilled with water if of suitable nat ure. 

 or if not . i an be put in after the filling. All tubes are 

 then clo-ed by >crew clamps around D in the experi- 

 mental tube-, or B in the blanks. The tube- are then placed in a 

 Miitable \\ater bath kept at constant temperature. Those con- 

 taining the animals should be agitated at inters al-. in the case of 

 m .ii-iin t ile animals, to prevent an accumulation of metabolic prod- 

 ucts and e\liaii-tion of the oxygen around them. When it is de- 

 fied to conclude the experiment, each experimental tube is in- 

 verted -e\eral times to insure uniform distribution of its oxygen 

 content and is then finally inverted, the animals being brought by 

 'oa\ ity into the section CplusZ). A screw clamp of suitable size is 

 then rapidly placed around the tubing B over the small interval 

 left between .1 and C. On screwing the clamp, A and C will be 

 found to mo\e apart readily and the walls of the tubing B are 

 at the -aim- time drawn together by the negative pressure thus 



1 P.. i. 



