NEUTRALITY OF THE TISSUES AND TISSUE-FLUIDS 279 



Solutions such as those of sodium bicarbonate, disodium phosphate 

 or sodium proteinate which conserve the neutrality of the water in 

 which they are dissolved are very frequently designated "Buffer- 

 solutions" from the resemblance of their action obliterating rapid 

 changes of hydrogen concentration to the action of a buffer on a vehicle 

 in obliterating dangerously sudden changes of velocity of motion. 

 Buffer-solutions are frequently employed now, and must necessarily 

 be more and more widely employed, wherever stable conditions of 

 environment are requisite, as in bacterial cultures, cultures of living 

 tissue in vitro, aquarium-media for marine or fresh-water organisms, 

 and artificial circulating media. 



An estimation of the very greatest importance in all disease-condi- 

 tions or metabolic disturbances which involve Acidosis is that of the 

 Alkali-reserve or neutraliz ing-power of the blood. When large quanti- 

 ties of "fixed" i.e., non- volatile acids are thrown into the blood the 

 sodium with which they combine is rendered unavailable for neutraliz- 

 ing other portions of acid or for binding carbon dioxide. The alkali- 

 reserve in such cases is diminished and the ability of the blood to 

 maintain its neutrality is proportionately impaired. A low alkali- 

 reserve is therefore, in general, a relatively hazardous condition. 



Various methods have been proposed for measuring the alkali-reserve, 

 the majority depending upon the fact that as the sodium bicarbonate 

 of the blood has been diminished and the uncombined carbon dioxide 

 stands in almost constant proportion to it, the carbon dioxide obtain- 

 able from the blood by a standard procedure is diminished. The 

 method suggested by Van Slyke, and now employed very widely, 

 consists in taking a sample of blood from a vein in the forearm and 

 introducing it into a vessel filled with the alveolar air of the patient 

 obtained by breathing and rebreathing into the vessel several times. 

 The blood is then shaken up with the alveolar air to bring it into equi- 

 librium with the carbon dioxide contained therein and a measured 

 sample, without loss of carbon dioxide, is introduced into a special 

 form of gas-burette (Fig. 13) and acidified with sulphuric acid to 

 decompose the bicarbonates. The chamber containing the sample 

 is now evacuated by means of a column of mercury and the gas which 

 is evolved is measured at atmospheric temperature and pressure. 



An alternative and perhaps preferable method which is, however, 

 somewhat less simple to manipulate, consists in directly analyzing the 

 carbon dioxide content of Alveolar Air obtained by rebreathing into 

 a closed vessel. When the alkali-reserve is low, the carbon-dioxide 

 content of the blood being diminished, the carbon-dioxide output 

 through the lungs and the partial pressure of carbon dioxide in the 

 alveolar air are correspondingly diminished. 



Another feasible method of measuring the alkali-reserve, or, which 

 comes to the same thing, the Neutralizing-power of tissue-fluids is that 

 which has been employed by Marshall in the analysis of Saliva. The 



