328 PROPERTIES OF THE COLLOIDAL CONSTITUENTS 



leave the stomach and penetrate the tissues an equivalent number of 

 hydrogen ions migrate from the tissues into the lumen of the stomach 

 and there combine with the chlorine ions to form Hydrochloric Acid. 

 In the first place the assumption of the differential permeability of 

 the stomach-wall for sodium and hydrogen ions is purely gratuitous 

 and has no foundation in direct observation, and in the second place 

 the theory would require the presence of food in the stomach before 

 acid gastric juice could be secreted, whereas, as Pavlov has shown, the 

 secretion of acid gastric juice may be excited reflexly without the 

 presence of any foodstuffs in the stomach. 



T. B. Osborne has, however, drawn attention to a mechanism where- 

 by an acid fluid may be elaborated through the intermediation of 

 Proteins. When Edestin is dissolved in sodium chloride solutions and 

 then precipitated by passing in a stream of carbon dioxide, it is found 

 that the precipitate contains an excess of combined hydrochloric 

 acid, while, on the other hand, an equivalent mass of sodium carbonate 

 or bicarbonate has been formed in the fluid and may be estimated by 

 titration with methyl orange. When, in other words, the excess of 

 sodium hydroxide is neutralized by carbon dioxide, this protein com- 

 pound of sodium chloride breaks up, setting free sodium hydroxide 

 and retaining hydrochloric acid in combination. A precisely similar 

 phenomenon occurs when Red Blood-corpuscles are repeatedly washed 

 with isotonic salt solution until the washings become perfectly neutral 

 and are then suspended in neutral sodium chloride solution and treated 

 with a stream of carbon dioxide. The external fluid becomes alkaline 

 and the blood-corpuscles become richer in chlorine (Giirber). In this 

 way hydrochloric acid is brought into combination with a non-diffusible 

 base, and may be subsequently separated from it by hydrolytic dis- 

 sociation, followed by the diffusion of the hydrochloric acid into the 

 surrounding medium, or in the particular instance under consideration, 

 into the gastric juice. We may infer, therefore, that the secretion of 

 an acid juice depends upon the existence in the secreting cells of a 

 protein which is capable of decomposing sodium chloride in the presence 

 of carbon dioxide. The appearance of the free hydrochloric acid in 

 the secretion being attributable to the colloidal, indiffusible character 

 of the protein base. 



THE SELECTIVE ACTION OF TISSUES AND THE " OLIGODYNAMIC " 

 ACTIONS OF HEAVY METALS. 



It is a universal phenomenon in living tissues that despite the fact 

 that the exact composition of the inorganic milieu is so definitely related 

 to their welfare and can depart so little from normality without induc- 

 ing disturbances of permeability, yet the relative proportions of the 

 various inorganic constituents of the protoplasm do not conform at 

 all to -.the proportions subsisting in the medium which they inhabit. 



