336 PRINCIPLES OF GENERAL PHYSIOLOGY 



After activity the cells are seen to be diminished in volume. Bunch (1900) 

 showed that, when the submaxillary gland is caused to secrete, there is a rapid 

 decrease in volume of the whole gland, although the simultaneous vascular 

 dilatation in itself produces an increased volume. 



In cells which have been fixed, the granules referred to stain with the so-called "acid," 

 that is, electro-negative dyes, such as eosin and acid fuchsin. They behave, therefore, like 

 electro-positive colloids, and in an opposite way to the general mass of the cell protoplasm ami 

 the nucleus. There is also frequently to be seen what appears to be a specially differentiated 

 part of the cytoplasm, known as " kinoplasm " or "ergastoplasm," staining deeply with 

 "basic" dyes. This is shown in Fig. 91. According to Laguesse and Delieyre (1912), the 

 dye known as Janus-green brings out the filaments of ergastoplasm in the fresh cell, so that 

 they seem to be present in the living cell, and not to be produced by the fixation pn 

 This dye also stains a little cap of matter on each zymogen granule, which is itself unstained. 

 Some further particulars with regard to morphological changes in gland cells will l)e found 

 below, in the discussion of the pancreatic secretion. 



That there is a change of permeability in the secreting cell is indicated by the 

 experiments of Garmus (1912) referred to above (page 140). Under atropine, 

 which paralyses the secretory process, the gland cells are less permeable to dyes 

 than when secreting under the influence of pilocarpine. According to Gildemeister 

 (1913), the cell membrane of the sweat glands becomes more permeable when 

 activity is brought about by stimulation of the nerves to the glands. Thi:. is 

 indicated by the diminution of galvanic polarisation, presumably due to increase 

 of permeability of the membrane to ions, in a way similar to that described above 

 in the case of Congo-red and parchment paper (page 161). 



According to Macallum (1911, p. 644), differences of adsorption, due to surface 

 tension, play a part in secretory processes. Taking the distribution of potassium 

 as an index to that of the other cell constituents which lower surface tension, he 

 finds, in secretory cells, that there is considerable accumulation of this substance 

 at the cell surface next the lumen. It seems possible that this fact may play a 

 part in the transfer of substances from the body of the cell to the lumen of the 

 duct, although it is difficult to understand how adsorbed substances can play a 

 part in the processes of osmosis or diffusion, since they are held by sin-face force* 

 In connection with the remarks made above (page 335) on the possible relation 

 between secretion, and absorption, it is interesting to note that, in intestinal cells 

 engaged in absorption, the greater accumulation of potassium is at the end ojip<>xit'~ > 

 to the lumen of the intestine. During absorption of fat, also, it has been noticed 

 that the cells of the intestinal villi show a greater accumulation of fat droplets at 

 their attached ends. 



THE GLOMERULUS OF THE KIDNEY 



It has long been known that when the arterial blood pressure falls below some 

 30 to 40 mm. of mercury the secretion of urine ceases. It occurred to Starling 

 (1899) that, if the liquid leaving the glomerular capsule is a filtrate from the blood 

 plasma, containing all the constituents of the plasma with the exception of the 

 colloids, then the blood pressure would be insufficient to effect the filtration unless 

 it were higher than the osmotic pressure of the colloids. This process would then 

 be similar to the filtration of a colloidal solution through Martin's gelatine filter. 

 Accordingly Starling prepared the filtrate of serum through such a filter, and 

 compared the osmotic pressure of the original serum against it, thus obtaining the 

 osmotic pressure of the colloids, which amounted to about 30 mm. of mercury. As 

 pointed out above, this was the first definite proof that colloids could hav> a 

 measurable osmotic pressure. Further support was given to Starling's view by 

 measurements of the difference between the pressure in the ureter and the arterial 

 pressure, when the former was gradually raised until secretion ceased. At this 

 point the ureter pressure was 92 mm. of mercury when the arterial pressure was 

 133 mm. of mercury, a difference of 41 mm. of mercury. It will readily be seen 

 that the rate of filtration under a given blood pressure will be increased by 

 reducing the osmotic pressure of the colloids by dilution, for example. Such a 

 dilution can be produced by the injection of hypertonic solutions, say of glucose, 

 into a vein ; the effect is the withdrawal of water from the tissues into the blood, 



