NEUTRALITY OF THE TISSUES AND TISSUE-FLUIDS 271 



discharge their functions under the stimulus of a definite positive or 

 negative pressure, acting like so many dams, to maintain the reservoir 

 of mineral constituents, heat, or bases at a certain height while the 

 inflow and outflow are equalized so that the height of the reservoir 

 does not progressively increase or decrease. We have in fact in each 

 case a number of balanced activities in dynamic equilibrium, a type of 

 mechanism which is repeatedly reduplicated in life-phenomena. 



Notwithstanding the fact that the mineral composition of mam- 

 malian blood-sera differs appreciably from that of sea-water only in 

 total concentration and in the relative content of a single constituent, 

 Magnesium, yet this latter difference renders sea-water, even when 

 diluted to isotonicity with blood-serum, far from a physiologically 

 neutral fluid for mammalian tissues. It has been shown by Burnett 

 that sterilized sea-water, rendered isotonic with blood-serum by 

 dilution, causes Glycosuria, considerable amounts of glucose appearing 

 in the urine when the sea-water is injected into the circulation of 

 rabbits. The same effect is brought about by Locke's or Ringer's 

 solutions, if magnesium is added to them in the proportion in which 

 it is present in sea-water. Hence diluted and sterilized sea-water 

 cannot be employed for surgical purposes as a substitute for Locke's 

 or Ringer's solution. 



THE NEUTRALITY OF THE TISSUES AND TISSUE-FLUIDS. 



The statements concerning the alkalinity of the blood which are to be 

 found in the physiological and medical literature of the last and early 

 part of this century are totally unreliable since they were based upon 

 the erroneous belief that it is possible to ascertain the reaction of such 

 a fluid as the blood by titration. The method of titration merely 

 informs us of the quantity of bases which are present either uncombined 

 or else combined with weak acids such as carbonic acid, which are dis- 

 placed from their compounds by the stronger acids used in titration. 

 If all of the bases are present in the free, uncombined form then, in 

 dilute solutions at all events, the true alkalinity or hydroxyl ion con- 

 centration may be fairly accurately estimated to be equivalent to the 

 amount of acid required for neutralization. But this is not at all the 

 case if. the bases are partially or wholly combined with weak acids, 

 because in that event the addition of the acid employed in titration 

 displaces the weak acid which, when uncombined, by reason of its 

 slight dissociability, ceases to affect materially the reaction of the 

 fluid, and the condition which we are seeking to measure alters con- 

 tinuously throughout the titration. Thus it is possible to estimate all 

 of the sodium in a solution of sodium bicarbonate by direct titration 

 with sulphuric acid, using Methyl Orange as an indicator, because the 

 carbon dioxide which is displaced by the sulphuric acid, is so slightly 

 dissociated in comparison with the acid used for titration that its con- 

 tribution to the final reaction of the mixture is negligible. Yet a 



