PRESIDENTIAL ADDRESS,* 751 



With the use of this method of determining differences in surface tension in 

 colls it is possible, in some cases at least, to ascertain whether this force plays a 

 part in both secretion and excretion, and evidence in favour of this view can be 

 found in the pancreatic cells of the rabbit, guinea pig, and in the renal cells of tho 

 frog. In the pancreatic cells there is an extraordinary condensation of potassium 

 salts in the cytoplasm of each cell adjacent to the lumen of the tubule, and 

 during all the phases of activity — except, it would appear, that of the so-called 

 "resting stage " — potassium salts occur in, and are wholly confined to, this part 

 of each cell. It is difficult to say whether they pass into the lumen with the 

 secretion and their place taken by more from the blood-stream and lymph, but 

 the important point is that the condensation of potassium salts immediately 

 adjacent to the lumen seems to indicate a lessened surface tension on the lumen 

 surface of the cell. 



According to Stoklasa 1 the pancreas of the pig is much richer in potassium 

 than in sodium, the dried material containing 209 per cent, of potassium and 28 

 per cent, of sodium, while the values for the dried material of ox muscle arc, 

 as he determined them, 182 and 0'26 per cent, respectively. It is significant that 

 in the pancreas this large amount of potassium should be localised as described. 



In the renal cells of vertebrates there is usually a considerable amount of 

 potassium salts distributed throughout the cytoplasm. These cells are always 

 active in the elimination of the element from the blood, and it is in consequence 

 not possible to determine whether there are differences in surface tension in 

 them. Under certain conditions, however, these can be demonstrated. In 

 the frogs which have been kept in the laboratory tanks throughout the winter, 

 and in the blood of which the inorganic salts have been, because of the long 

 period of inanition, reduced to almost hyptonic proportions, the renal cells 

 are very largely free from potassium. When it is present it is usually diffused 

 throughout the cytoplasm. If now a few cubic centimetres of a decinormal 

 solution of potassium chloride be injected into the dorsal lymph sacs of one of 

 these frogs, and after twenty minutes the animal is killed, appropriate treatment, 

 with the cobalt reagent, of a thin section of the fresh kidney made by the carbon 

 dioxide freezing method, reveals in the cells of certain of the tubules a conden- 

 sation of potassium salts in the cytoplasm immediately adjacent to the wall of 

 the lumen. There is also a very slight diffuse reaction throughout the remainder 

 of the cytoplasm, except in that part immediately adjacent to the external 

 boundary of the tubule. In these cells the potassium injected into the lymph 

 circulation is being excreted, and the condensation of the element at or near 

 the surface of the lumen is evidence that there the tension is lees than at the 

 other extremity of the cell. 



These facts are in their significance in line with some observations that I have 

 made on the absorption of soluble salts by the intestinal mucosa in the guinea-pig. 

 When the ' peptonate ' of iron was administered in the food of the animal it was 

 not unusual to find that in the epithelial cells of the villi the iron salt was dis- 

 tributed through the cytoplasm, but its concentration, as a rule, was greatest in 

 the cytoplasm adjacent to the inner surface of the cell, from which it diffused 

 into the underlying tissue. Here also, inferentially, surface tension is lower 

 than elsewhere in the cell. 



It would perhaps be unwise to form final conclusions at this stage in the 

 progress of the investigation of the subject, but the results so far gained tempt 

 one to adopt as a working hypothesis that in the secreting or the excreting cell 

 lower surface tension exists at its secreting or excreting surface than at any other 

 •point on the ceil surface. How this low surface tension is caused or maintained 

 it is impossible to say, but, whatever the solution of the question may be, it is 

 important to note that we must postulate the participation of this force in renal 

 excretion in order to explain the formation of urines of high concentration. Theso 

 have a high osmotic pressure, as measured by the depression of the freezing point, 

 while the osmotic pressure of the blood plasma determined in the same way is low. 

 On the principle of osmosis alone, as it is currently understood, this result is 

 inexplicable, for the kinetic energy, as required in the gas theory of solutions, 

 should not be greater, though it might be less, in the urine than in the blood. It 



1 Stoklasa gave the values in K 2 and Na„0. 



3c2 



