NON-NEOPLASTIC LATE EFFECTS 183 



The direct mechanical importance of ground substance for properties Hke 

 capillary pinocytosis or emigration is apparent. The electrostatic effect on the 

 diffusion of positive ions is demonstrated by the work of Joseph and colla- 

 borators (1952), In the polyanionic matrix, fixed by a tight fibrous network, 

 e.g. of the symphysis pubis of guinea-pigs, the mobihty of K ions appeared to 

 be halved. Under the influence of sex hormones the relaxation of this tissue 

 increases ionic mobihty to normal. It must be important to know, if this 

 extracellular inhibition of cationic mobility may be generalized as a contribu- 

 tion to the slo wing-up of ionic capillary exchanges in ageing tissues, or also in 

 tissues where the ground substance fibres quotient had been decreased by 

 irradiation. 



The turnover of acid mucopolysaccharides, sulphated or not appears to be 

 a few days or less (Dorfmann and Schiller, 1960), but m older animals the 

 composition of the mixture of acid mucopolysaccharide is changed and the 

 rate of production is slowing down. According to Korenchevsky quoting Sobel 

 and others (Bunting and Bunting, 1953 for human aorta), the decrease in the 

 ratio hexosammes/collagen is characteristic for the ageing of many tissues 

 including aorta in rats and also in man. 



Sobel and Marmorston (1956) and Sobel et at. (1960) have already shown 

 that the decrease of the quotient ground substance/fibres is much accelerated 

 in irradiated rats. This held for aorta, lungs, skin and sternum, but not for 

 caval veins. The radiative ground substance deterioration is of vital impor- 

 tance and is mainly expected in the vascular system. We will have the oppor- 

 tunity later of discussing the mucopolysaccharides gel-filtration layer, 

 preventing pressure infiltration of the aortic wall by large molecules. For 

 arterioles, capillaries and venules much evidence can be found in recent 

 reviews; I might quote Casarett (1959): "the only wide-spread histopatho- 

 logical effect of a permanent and progressive type, which could be traced 

 continuously from the time of radiation exposure to the time of death was the 

 effect on small blood vessels, especially arterioles and capillaries". Further, 

 Rhoades (1948) said that vascular changes, following treatment with ionizing 

 radiation, are^ probably secondary to changes in the connective tissue, 

 Surrounding the vessels. And lastly, it must be concluded from the work of 

 Bargmann (1958), Gersh and Catchpole (1961), lUig (1962) and especially of 

 Magno and Palade (1961) that capillary permeability in many regions is 

 chiefly determined, not by the endothelium but by the basement membrane, 

 surromiding the capillary as a formation of the ground substance. 



It is in these, still somewhat mysterious, basement membranes that I 

 venture to suspect an important front where ageing and also radiation effects 

 may have serious delayed consequences. 



In many organs the basement membranes become markedly thicker 

 during ageing (Gersh, 1952) and this must influence blood/ceU exchange. As 



