186 STUDIES ON RESPIRATION. II 



is an average for that period, and if the rate is changing, it is evi- 

 dent that this average rate will in general occur somewhere near the 

 middle of the period. Hence in drawing the curve the points are 

 taken in the middle of each period. The other curves are made in 

 the same way but the periods are not indicated. 



After exposure to the reagent has begun, the intervals between 

 periods of measurement are included in the total time of exposure 

 to the reagent, because even when the material is momentarily- 

 lifted out, it remains covered by a film of the reagent. The rela- 

 tive rate of respiration for each period is obtained by dividing the 

 rate for that period by the normal rate. This applies to all the sub- 

 sequent work. 



The main part of the work was done with ether. Various concen- 

 trations between 0.37 and 1.46 per cent (by volume) were tried in the 

 beginning but as these had little or no effect, higher concentrations 

 were employed. A slight increase of respiration, which lasted for 

 some time, was obtained with 1.46 per cent ether. With 3.65 per cent 

 three distinct types of results were obtained. The first and most 

 common type was a sharp rise in respiration in the first period, fol- 

 lowed by a gradual decrease (Fig. 2, Curve A), so that at the end of 

 half an hour the rate was slightly below normal. From this point 

 on the rate decreased more slowly, reaching about 60 per cent of the 

 initial rate at the end of 80 minutes. A second type gave a curve 

 with a flattened top having the maximum rate of respiration in the 

 third or fourth period. Only very few experiments showed this type. 

 The third type never gave a rise, but always a slow decrease from the 

 beginning (Fig. 2, Curve B). 



These three types were constant in the sense that each culture 

 always gave only one result, no matter how many experiments were 

 made. Though the cultures were grown under identical conditions, 

 yet this difference in behavior was always noted. 



A saturated solution of ether was also tried. As this is approxi- 

 mately 7.3 per cent by volume, the latter designation has been used 

 for the sake of convenience. With 7.3 per cent only one type of result 

 was noticed, even when the same cultures were used with which dif- 

 ferent results had been obtained with 3.65 per cent. A very pronounced 

 increase was noticed in the first period followed by an almost equally 



