30 Hugh Davson 



conditions of injection of fluid into the tissue, is it possible to 

 speak of free fluid in the extracellular spaces. The nature of 

 the collagen and mucoid in these tissues may therefore exert 

 some effect on the water content of the tissues. In general, it 

 would seem that acute changes in this tissue extracellular 

 water are the result of changed factors of capillary filtration 

 and reabsorption, but it may well be that the long-term 

 steady-state level is influenced by the amount of mucoid in the 

 tissue. This presumably exerts its Gibbs-Donnan difference 

 of osmotic pressure, drawing fluid to it; the tendency is 

 opposed by the structural rigidity of the tissue, so that a 

 steady state is established, in contrast to the cornea where the 

 rigidity of the system is inadequate to permit a steady state, 

 a continuous secretory activity being necessary, and made 

 possible by the presence of cellular membranes lining the 

 tissue. 



The possible ways in which the water compartments of the 

 body may be altered with age become evident from this 

 general review; thus, the activity of the ion-transporting 

 mechanisms of the cells tends to oppose a normal tendency 

 to cell oedema, with the result that a steady state is main- 

 tained with the cells having a characteristic ionic make-up and 

 percentage of water. A decrease in the metabolic activity of 

 the cells may be expected to result in the penetration of salt 

 and water into the cells; hyperactivity, on the other hand, 

 may cause a shrinkage of the cells, but the extent of this will 

 be limited by the demands of electrical neutrality; excessive 

 excretion of the Na+ ion must be associated with excretion of 

 some anion or with accumulation of K+; in the latter event 

 there will be no change in osmolarity, whilst the former process 

 is limited by the availability of diffusible anions. It seems 

 unlikely that a cellular dehydration could result from hyper- 

 activity of this sort, and it seems more likely that dehydration 

 of cells might be due to a loss of the indiffusible anions, 

 collectively indicated as A" in Fig. 4, but actually consisting 

 of proteins, organic phosphates, etc. If these were replaced by 

 such diff'usible anions as CI" and HCO3-, then the process of 



