FUNCTIONS OF SWIMBLADDER OF FISHES. IO/ 



the blood and the cells. In such a physiological system it is 

 necessary that a definite amount of blood should pass through 

 an organ; it must give a definite oxygen tension to the organ 

 and in so doing becomes reduced. The amount of that reduction 

 varies with the need of any particular organ. The question 

 arises is there evidence that each or any organ of the body is 

 so far master of its own metabolism that it can force the vascular 

 system to give it the oxygen which it requires. Gaskell (1880) 

 stated this question years ago. Evidence has ever been increas- 

 ing since his time. Gaskell and other more recent workers 

 have shown that certain metabolic products, especially acids, 

 including carbon dioxide and lactic acid, have the power of 

 distending blood vessels. Dale and his colleagues (1911) have 

 also shown that beta- iminazolylethylamine, a body so closely 

 bound up with the physiology of protoplasm that it is liberated 

 by the splitting off of carbon dioxide from histidine, produces a 

 powerful dilatation of the blood vessels. 



Barcroft (1914) and other investigators have shown that the 

 affinity of hemoglobin for oxygen is very sensitive to small 

 changes in acidity or alkalinity. The effect of an increased 

 acidity is to lessen the concentration of the oxygen which is 

 held in solution by the hemoglobin. Barcroft has also shown 

 that the influence of acids depends upon the change in the hydro- 

 gen ion concentration which they cause in the blood. Bohr 

 (1896) found experimentally that when the oxygen tension is low, 

 an increase in the carbon dioxide tension tends to dissociate 

 oxy-hemoglobin. Since these conditions prevail in the capil- 

 laries, the presence of carbon dioxide in increased amounts 

 facilitates the liberation of oxygen. Barcroft maintains that it 

 is the "reaction " of the blood that has the effect of varying the 

 dissociation of oxygen from oxy-hemoglobin. The more acid 

 the blood contains, or the more acid the "reaction" due to the 

 increased amounts of lactic acid or an increased tension of carbon 

 dioxide, the more readily does the oxy-hemoglobin undergo dis- 

 sociation. 



Two experiments described by Barcroft show that the addition 

 of acids greatly accelerates the reduction of blood and that the 

 concentration of the acids necessary to produce approximately 



