108 



SCIENCE 



[N. S. Vol. XLIV. No. 1125 



the method can be modified as follows. One 

 end of the glass tube has a paraffined plug hav- 

 ing two holes, while the other end has the 

 usual paraffined rubber tube. One hole can be 

 sealed shut if no stem is to protrude, while in 

 the other hole a small glass tube containing the 

 required number of drops of indicator is in- 

 serted with a solid glass plunger of equal 

 diameter adjoining, and protruding from the 

 plug. At the end of a given time the indi- 

 cator is pushed into the solution by means of 

 the airtight plunger and the reading is made 

 rapidly. In such a modification, control tubes 

 must be depended upon to give the hydrogen 

 ion concentration of the solution at the start of 

 the experiment, and, moreover, only one read- 

 ing can be made from a single tube. 



Pure block tin collapsible tubes have been 

 found to be very useful but are very difficult to 

 seal as compared with the paraffined rubber 

 which is easily sealed. Experiments with 

 seeds were run for an hour without any change 

 in the control, and even though it may be pos- 

 sible to run experiments a much longer period 

 without change in the control, yet it appears 

 advisable to cut down the time of an experi- 

 ment whenever possible; this the new method 

 permits. 



In making up buffer solutions, 5 the writer 

 has found it advisable to recrystallize chem- 

 ically pure salts several times, and whenever 

 possible it is best to check up the accuracy of 

 the buffer solutions with the aid of the hydro- 

 gen electrode. 



The writer has found that a constant source 

 of light such as has recently been described in 

 Science 6 is almost indispensable for this work. 

 By using seeds with the coats removed and 

 a relatively small amount of solution a color 

 change can easily be detected within five 

 minutes. 



By this method we can compare the respira- 

 tion of organisms in different solutions with 

 great accuracy without knowing the actual 

 amounts of CO„ given off. We need only to 

 compare the times required to produce the 



5 Miehaelis, L., ' ' Die Wasserstoffionen-KoiLzen- 

 tration. ' ' 



e Science, N. S., 42: 764, 1915. 



same change of color in the solutions. If we 

 use a substance in solution which affects the 

 change of color in the indicator, this substance 

 must be added to the set of buffer solutions. 

 If, for example, we are studying the effect of 

 NaCl on the respiration of roots we put one lot 

 of roots into a solution of Nad and another 

 lot into distilled water. We then prepare a set 

 of buffer solutions to which we add N"aCl so as 

 to make its concentration the same as in the 

 solution containing the roots. We add the 

 same amount of indicator to the solution con- 

 taining the roots and to the buffer solutions, 

 and the changes of color are then comparable. 

 We proceed in the same way with the distilled 

 water or with any other solutions employed. 



If we wish to know the actual amounts of 

 C0 3 given off we may calibrate the indicator 

 by a very simple method, as yet unpublished, 

 due to Henderson and Cohn. We may then 

 use an indicator which passes through a well- 

 defined series of color changes as the amount 

 of CO„ increases. By observing these changes 

 we can plot the amount of CO;, against time. 

 The resulting curve enables us to study the 

 dynamics of the reaction and this is of primary 

 importance for an understanding of the proc- 

 esses involved in metabolism. 



SUMMARY 



1. Respiration may be accurately followed by 

 observing changes in the color of indicators 

 added to solutions which contain organisms. 



2. Exceedingly small amounts of CO. may be 

 determined in this way with great accuracy. 



3. As changes in color often occur in five 

 minutes, the experiments may be shortened so 

 as to exclude pathological changes in the 

 organisms. 



4. The simplicity of the apparatus makes it 

 possible to carry on a large number of experi- 

 ments at the same time. 



5. The amounts of CO. produced in succes- 

 sive intervals can be determined without dis- 

 turbing the organism. This enables us to 

 study the 'dynamics of the process. 



A. R. Haas 

 Hakvakd University, 

 Laboratory op Plant Physiology 



