1 9 1 9] HA A S—RESPIRA TION 3 8 1 



always used at the same temperature as that of the water bath. 

 After the tubes containing the Laminaria in sea water had been at 

 16° C. from half an hour to an hour, the solution was poured out 

 of each tube and replaced by fresh sea water at 16° C. This was 

 repeated several times before beginning an experiment. 



After a tube containing Laminaria in sea water had been 

 clamped off so as to include a small bubble of air which could be 

 used as a stirrer, and had been exposed to 16° C. for a definite 

 period, it was removed from the bath. The solution was slightly 

 stirred by inverting the tube a few times; the clamp was then 

 opened and the solution rapidly poured into another empty tube 

 to which the same number of drops of indicator (phenolsulphone- 

 phthalein) had been added as was added to the buffer solutions (7). 

 In order to mix the solution with the indicator it was stirred as 

 described, and was then compared with buffer solutions of a known 

 PH value which contained the same amount of indicator. 



The use of a small bubble of air as a stirring agent was found to 

 be very convenient, and when compared with the use of paraffined 

 glass globules as stirrers was found to introduce no error of any 

 importance. 



The buffer solutions (27) were made up by mixing M/15 

 Na2HP04 and M/15 K.H2PO4 in various proportions. They were 

 of the same diameter as those containing the alga. A o.oi per 

 cent aqueous solution of phenolsulphonephthalein served as the 

 indicator of the PH values. The indicator solution was used at 

 the rate of 5 drops in 10 cc. of solution. A correction (30) of 

 o . 30 for the salt error of the indicator in sea water was subtracted 

 from the observed readings of the PH value of sea water. The use 

 of a constant source of light (the "Daylight" lamp) permitted 

 observations to be made in a uniform manner. The decrease in 

 PH, which results from the production of CO2, served as a criterion 

 of the amount of respiration. 



In all the experiments, each tube was observed for a number of 

 periods (always of the same length) for each piece of material, 

 until it was evident that the rate of respiration had become prac- 

 tically constant. Several of the tubes were then used as con- 

 trols, while to the others was added the sea water containing the 



