164 



PRINCIPLES OF GENERAL PHYSIOLOGY 



An important series of papers has been published by Demoor and his 

 coadjutors (1907) on the relation of secretory organs, such as the liver, kidney, 

 and subrnaxillary gland, to the osmotic pressure of the liquid perfusing their 

 blood vessels. The discussion of some of these facts will be found in Chapter XI. ; 

 in this place one or two suggestive points only will be referred to. 



The cells lining blood vessels, like other living cells, are no doubt subject to 

 changes of volume in response to changes in the osmotic pressure of the blood. 

 According to Demoor, the effect of this change in volume will be to alter the 

 lumen of the vessel, so that, other things being equal, a fall in the osmotic pressure of 

 the blood causes a swelling of the lining cells of the blood vessels and a consequent 

 narrowing of the lumen. This fact has special application to the function of the 

 kidney. In the case of the liver (1907, p. 32) it was found that the rate at 

 which 1*5 per cent, sodium chloride passed through was greater than that of 

 0'6 per cent., while 0*9 per cent, was intermediate. A solution of a concentration 

 of 0'6 per cent, became more concentrated and one of 1'5 per cent, became diluted 

 in its course. So that it is clear that the cells take up water from a hypotonic 

 solution and that the swelling so caused obstructs the circulation, and vice versa. 

 How far the effect is due to the liver cells themselves and how far to the lining 

 cells of the blood vessels is not quite clear, but it seems probable that the former 

 is the chief factor. We call to mind that the liver capillaries send branches 

 into the substance of the liver cells (Schiifer, 1902), so that the capillaries are 

 devoid of walls in certain places. The reactions described disappear when the 

 semi-permeability of the cells is destroyed by sodium fluoride. 



Similar phenomena were found in the pulmonary circulation (page 50), and it 

 seems probable here that changes in the volume of the lining cells of the blood 

 vessels might play the chief part. 



In the kidney, we meet with the same facts as regards the rate of flow of 

 blood. The rate of secretion falls also with hypotonic solutions and rises with 

 hypertonic, as had been observed by Starling (1899). But investigations on 

 the changes of volume of the kidney show that the organ, as a whole, ,y//W/,s- 

 when a hypertonic solution is perfused, and vice versa (page 69). Owing to the 

 complexity of the factors involved here, discussion of the question will best 

 be postponed to Chapter XI. 



We have seen why it is necessary for animal cells to be in contact with a 

 liquid of the same osmotic pressure as themselves. There is evidence, moreo\rr, 

 that when exposed to the action of a liquid of a different osmotic pressure, 

 they are able to accommodate themselves to a certain extent by change in 

 their own osmotic concentration. For example, it appears that the cambium 

 cells of trees, as the external pressure upon them increases, produce osmotically- 

 / active substances in order to raise their own osmotic pressure. 



The body fluids, including the blood, of marine invertebrates, have the same 



I osmotic pressure as the sea water in which they live. If certain of these organisms, 



' Maia verrucosa, a crustacean, for example, is placed in concentrated or diluted 



sea water, it is found that the body fluid takes the same osmotic pressure as 



the solution; the following data from Fredericq's paper (1885) will show this: 



The regulation is apparently effected through the cells of the gills. Since the 

 changes in question do not permanently affect the animal, it is plain that 



