The Relation of Excised Muscle to Acids, Salts, and Bases. 279 



final equilibrium of the muscle system. It therefore seemed necessary, in 

 order to obtain an accurate record of the phenomena exhibited in an excised 

 muscle in a medium with a reaction near the neutral point, to use some 

 more accurate method of controlling and measuring the acidity or alkalinity 

 of the experimental fluid. The scale obtained by taking " normality " as a 

 measure of acidity is not sufficiently fine to investigate the muscle behaviour 

 at a critical point such as the neutral point of the medium, or the iso-electric 

 point for the muscle. It was, therefore, decided to investigate this critical 

 zone by means of Sorensen's solutions (24). This method not only gives a 

 delicate means of adjusting the hydrogen ion concentration of a solution to 

 any desired value, but also, by means of the " buffers," keeps this value steady 

 when foreign bodies (such as muscles) are put into the system. 



In Sorensen's papers there are two different units which have been used to 

 express the concentration of hydrogen and hydroxyl ions in a system. The 

 units C H or O h mean respectively the number of grammes of free hydrogen 

 ion or hydroxyl ion present in a litre of solution. They are always given as 

 powers of the base 10, and always have, for obvious reasons, a negative sign 

 to the index. The other units used, expressed by the general term P H , are 

 the logarithms of the values C H and, for general convenience, the negative 

 sign is usually omitted. In distilled water C H = C h = 10 -7-1 , or P H = 7"1, 

 and Pqh = 7"1. Now in any solution P H + P h = 14 - 2, therefore, as 

 Ph increases,, P h decreases. Prom this it follows that if in any solution 

 P H < 7'1, the hydrogen ions predominate and the solution is acid ; if 

 P H > 7'1, the hydroxyl ions predominate and the solution is alkaline. 



The curves obtained by measuring the reaction of a solution by Sorensen's 

 system, and plotting this value against the final equilibrium weight of 

 a muscle immersed therein, are given in fig. 2. The curves in both figs. 1 

 and 2 are of the same type, i.e. they are curves obtained by plotting acidity 

 (or alkalinity) against final equilibrium. They differ in their method of 

 measuring acidity. In fig. 1 acidity is measured on the comparatively 

 rough scale of " normality," i.e. on the titration value of the solution. In 

 fig. 2, the actual concentration of the hydrogen ion in the solution is taken 

 as the measure of its acidity. As the points — - 01 N and +O01 N in fig. 1 

 correspond to the points P H = 11 and P H = 3, respectively, in fig. 2, it can 

 be seen that the critical zone on the curve in fig. 1 has been expanded over 

 a considerably wider area in fig. 2, and can therefore be studied with 

 correspondingly greater accuracy. 



The data for making the Sorensen solutions were taken from the chart 

 figured by Walpole (25). The acetate, phosphate, and borate mixtures were 

 used, and by this means a range of P H from 3 to 11 was examined. The 



