COMPARATIVE STUDIES ON RESPIRATION. 



XIII. An Apparatus for Measuring the Production of 

 Minute Quantities of Carbon Dioxide by Organisms. 



By MARIAN IRWIN. 



{From tltc Laboratory of Plant Physiology, Harvard University, Cambridge) 



(Received for publication, June 28, 1920.) 



Osterhout^ has described an apparatus by means of which the pro- 

 duction of small quantities of carbon dioxide by organisms may be 

 measured at short intervals. In this apparatus air is caused to cir- 

 culate through a tube containing the organisms and then into a tube 

 containing an indicator, the color changes of which are compared 

 with buffer solutions containing the same amount of indicator. 



The purpose of the present article is to describe a modified appara- 

 tus devised by the writer. 



The whole apparatus, with the exception of a short piece of rubber 

 tubing, is made of glass. In order to prevent leakage the joints and 

 glass stop-cocks are ground with special care. 



Fig. 1 shows a sectional view of a portion of the apparatus. The 

 tube O contains the organisms and the tube I contains an indi- 

 cator. These tubes are connected to the apparatus by ground joints. 

 When the stop-cock S is opened, and the stop-cocks Si and S2 are 

 closed,- the air is allowed to pass from the tube O containing the organ- 

 isms to the tube I containing the indicator.^ When S is closed and Si 

 and S2 are opened, the air passes from O to I through N which contains 

 lumps of sodium hydroxide for the absorption of carbon dioxide. The 

 ground joint J allows the apparatus to be disconnected."* The dotted 



1 Osterhout, W. J. V., /. Gen. Physiol, 1918-19, i, 17. 



" A single three-way stop-cock may be used in place of S, S] and S2 in order 

 to avoid dead spaces. 



^ The indicator tube and the inlet tube within it are made of Pyrex glass. 



^ It may be desirable to make the entire apparatus of Pyrex glass in which 

 case the ground joint J may be transferred to the right of S. This facilitates 

 the substitution of tubes of various sizes in place of O. 



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