480 Trans. Acad. Set. of St. Louis. 



death concentration, and on the other, one in which the 

 health of the alga remained practically uninfluenced. 



The reagents used were the best that could be obtained. 

 Guaranteed reagents could not be had in every instance and 

 " c. p." substances were then employed. The conditions un- 

 der which the work was conducted rendered it next to impos- 

 sible to use solutions standarized by titration or by gravimet- 

 ric methods. The solutions were made therefore by careful 

 weighings of the dried salts or the pure crystals, special pre- 

 caution being observed with those salts losing water of crj^s- 

 tallization upon desiccation. Stock solutions were made up 

 in sea water as .2, .3, or .4 normal (gram equivalent), de- 

 pending upon the strengths supposedly required, as demon- 

 strated by the preliminary experiments. From the above 

 stock solutions the necessary dilutions were prepared as re- 

 quired. The experiments were arranged in only three exten- 

 sive series, so that as many experiments as possible would be 

 conducted under practically similar conditions. The limits of 

 the dilutions used with the substances here reported were .4 

 and .001, gram equivalent. With some salts .2 or .3 N 

 was the highest concentration tested. Numerous control ex- 

 periments with bits of the algae under precisely similar con- 

 ditions, with the exception of the chemical substances tested, 

 were constantly run as parallel series. 



Experimental Results. In Table III the first considerable 

 series of results obtained, those at Woods Hole, are ofiven. 

 These results are expressed in decimals of a normal solution. 

 The series includes all of the toxic agents used at the time 

 with the exception of a few acids and salts of heavy metals, 

 which have been reserved for a later report. The concentra- 

 tions given in the table are those which practically represent, 

 under the conditions of the experiment, the mean health con- 

 centration of the algae used during (in this case) three days. 

 Tabulations were first made for each of the four algae used, 

 giving the highest concentration at which the alga remained 

 healthy, or, at most, was only slightly injured, and then the 

 averases of these concentrations have been taken for the sen- 



