No. 630] SHOETEB ARTICLES AND DISCUSSION 91 



out over the reefs to the northward the color index was 3.9 

 (8.6 per cent, yellow), that of the ocean beyond the reefs about 

 3.5 (7 per cent, yellow). 



W. J. Crozier 



Physiological Laboratory, 

 College of Medicine, 



University or Illinois. 

 June, 1919 



A SIMPLE METHOD OF MEASURING THE RATE OF 

 RESPIRATION OF SMALL ORGANISMS 



In view of the widespread interest at the present time in the 

 subject of respiration in the lower organisms, it is thought that 

 the following simple method of measuring the rate of carbon 

 dioxide production in small non-aquatic animals and plants 

 may be found useful not only by teachers who desire a quantita- 

 tive method suitable for class instruction but also by investiga- 

 tors who wish, without any material sacrifice in accuracy, con- 

 siderably to simplify the various procedures at present followed 

 in making determinations of small amount of C0 2 . The appa- 

 ratus required may readily be constructed by anyone in a few 

 minutes out of materials easily obtainable, and with it, it is 

 possible to measure, with a probable error well within the normal 

 uncontrollable range of variation of the material likely to be 

 studied, a few thousandths of a milligram of carbon dioxide — 

 an amount equal to that given out at ordinary temperatures by 

 a sprouting grain of wheat in perhaps three or four minutes and 

 by a house-fly in one or two minutes. It would be relatively 

 easy still further to increase the delicacy of the method, though 

 the gain in sensitiveness would be at the expense of the simplicity 

 which in its present form is its chief recommendation. 



The method is based upon the well known indicator methods of 

 Haas 1 and of Osterhout, 2 but unlike the first, it is applicable to 

 small non-aquatic organisms, and unlike the second, it involves 

 the use of apparatus so simple in construction that it can be 

 duplicated any desired number of times and can therefore be 

 used even by large classes of elementary students. Furthermore, 

 provision is made not only for the comparison of relative rates 

 of carbon dioxide production but also for the measurement of 

 absolute amounts. Simplicity is secured by taking advantage of 



1 Haas, A. E., Science, 1916, XLIV, 105. 



2 Osterhout, W. J. V., J. Gen. Physiology, 1918, I, 17. 



