218 PRINCIPLES OF GENERAL PHYSIOLOGY 



is the fact that the blood passing by crossed circulation from the heart of one dog-H.-h to lli.it 

 of another had no effect on the latter when the former was inhibited by the vagus nerve. But, 

 in experiments of this kind, negative results are less convincing than positive out >. 



Cfdarine. Turning our attention to anions, perhaps the most striking action is 

 that of chlorine on the central nervous system, according to the work of von Wyss 

 (1906). When sodium bromide is given in large doses, the chlorine content of the 

 blood can be reduced to one-third. The exact cause of this is disputed, but the 

 interesting point is that, at this stage, characteristic symptoms of paralysis set in. 

 According to von Wyss, these symptoms are not due to accumulation of bromine, 

 but to loss of chlorine, since they are rapidly cured by giving sodium chloride. 

 Moreover, while ammonium chloride is effective, sodium nitrate or sulphate or 

 magnesium sulphate is without action. Grilnwald (1909) obtained similar results 

 by depriving rabbits of chlorine in their food and administration of diuretics. 

 The mechanism of this phenomenon cannot be said to be altogether clear. 



Carbon Dioxide. Whether carbon dioxide or CO 3 " ions have any special 

 action on cell processes apart from that of the hydrogen ion also present in 

 solutions of carbon dioxide, is doubtful. It is held by some, for example, Laqueur 

 and Verzar (1912), that carbon dioxide as such has an exciting effect on the 

 respiratory centre, but the experiments are not convincing (see Chapter XXI.). 

 Rona (1912) stated that it has a similar one on the movements of the intestine. 

 The addition of sodium bicarbonate to a saline solution containing neither 

 bicarbonate nor phosphate, caused the movements of an excised intestine to 

 change from an irregular character to a perfectly regular one. This was 

 apparently not due to diminution in hydrogen ion concentration, since the 

 addition of bicarbonate had the same effect if its solution were previously brought 

 to the same hydrogen ion concentration as the solution to which it was added. 

 Also the production, by sodium hydroxide, of the same degree of alkalinity as 

 that caused by the bicarbonate, with glycine as "buffer," had no effect. The 

 result is held to be due to CO 3 " ions or to H CO 3 itself. 



SALTS OF WEAK ACIDS WITH WEAK BASES 



When a strong acid is added to a strong base in dilute solution, there is a 

 considerable fall in the electrical conductivity of the mixture as compared with the 

 sum of those of the two reagents separately. Since the salt formed is dissociated 

 to as great a degree as the acid or base, the diminution must be due to the 

 disappearance of the fast moving ions H* and OH'. 



For example, the conductivity of a 0'05 molar hydrochloric acid at 21 '8 is 17,945 reciprocal 

 megohms ; that of a similar concentration of sodium hydroxide is 9,695 reciprocal megohms ; 

 together 27,640, whereas 0'05 molar sodium chloride is only 4,995. In the solution of the salt 

 there are, per 20 litres, 1 molecule of Cl' ions and 1 molecule of Na' ions, together 2 moleculr>. 

 very nearly ; in 20 litres of hydrochloric acid, 1 molecule of H' ions and 1 molecule of Cl' ions ; 

 in 20 litres of sodium hydroxide, 1 molecule Na' ions and 1 molecule OH' ions ; so that, if 

 uncombined when mixed, there would be in all 4 molecules. But, even if we double the value 

 of the conductivity of the sodium chloride solution to allow for this, we only have 9,990, 

 instead of 27,640. It is evident that the diminution is only partially due to the disappearance 

 of H' and OH' ions in combination as water, but that the slower rate of migration of the Na' 

 and Cl' ions also plays a part. 



Again, if we neutralise a weak base, such as aniline, with a strong acid, we 

 get a diminution of conductivity, or if a weak acid is neutralised with a strong 

 base. 



On the other hand, if we take a weak base and a weak acid, the conductivity 

 of the salt is higher than the sum of those of the base and acid together. This 

 is because the salt is more highly dissociated, electrolytically, than either the base 

 or the acid, so that there is an actual increase in the number of ions present. 



It is not easy to see why, to take a specific case, the compound of the acetic anion with 

 hydrogen ion is very little dissociated, whereas when it is combined with the cation of aniline 

 there is considerable dissociation. 



The fact is probably of some importance in physiological processes. The 

 organic acids and bases produced in cell metabolism are for the most part of 

 the weak class, that is, very little electrolytically dissociated ; when they combine, 



