466 PROCEEDINGS OP THE AMERICAN ACADEMY, 



course show a diflferent adjustment. The most difficult preliminary 

 problem in the plan of experimentation was the determination of a 

 common physico-chemical condition for comparison. If solutions of the 

 salts here used be so made as to contain equal molecular concentrations, 

 they will still differ in osmotic concentratioji (the latter term used as by 

 Hamburger, :02, p.l4). Both of these factors are physically active in 

 any given solution, and biological experiment has shown that they are 

 also distinguishable in their physiological action. To facilitate inference 

 from effect to cause, it seemed advisable to eliminate if possible one of the 

 two factors. There is, in general, a closer correspondence between the 

 intensity of physiological action and the osmotic concentration of a solu- 

 tion than there is between physiological effect and the molecular concen- 

 tration producing it. Hence the desired elimination of a factor was most 

 easily accomplished by experimenting, in the beginning at least, with 

 solutions of equal osmotic concentrations. The molecular concentrations 

 of course varied, and differences (or equalities) in the effects obtained 

 could be interpreted accordingly, other conditions being alike. Curves 

 (p. 473), plotted from the mean results so obtained, represent directly the 

 variation in effects which was produced by variation in the molecular 

 concentration of each salt. 



Five series of experiments were made, each series representing the 

 simultaneous application of the above selected salts. These series are 

 designated both in the tables which follow and in the curves on p. 473 by 

 the Arabic numerals 1 to 5. Excepting the curves for series 5, the Roman 

 numerals I, II, III, IV, signify potassic chloride, sodic chloride, calcic 

 chloride, magnesic chloride, respectively. The effects of different salts 

 at nearly equal osmotic concentrations would be represented by an addi- 

 tional set of curves (not shown) connecting points numbered with the 

 same Arabic numerals (excepting the 5's, which represent different molec- 

 ular concentrations of calcic chloride). Between the points designated by 

 the same Arabic numerals, e.g., all the I's, the secondary curves should 

 be so drawn as to connect these points of equal osmotic pressure in the 

 order of their highest mean results. This order illustrates the variation in 

 mean results when osmotic pressures are equal, better than connection in 

 the order of concentration would. However, either method of connection 

 shows the great lack of parallelism between the curves and the axis of 

 abscissas, and this is the point of importance. 



To make such solutions, I took seven tenths as much of a molecular 

 weight of calcic chloride or magnesic chloride as of potassic chloride or 

 sodic chloride. The limits of error on the biological side are so wide 



