SECRETION AND EXCRETION 333 



give us the basis for an understanding of certain changes in the 

 function of the kidney in pathological and senile conditions, in which 

 the filtering membrane is inelastic. From what has been said it 

 cannot be ruled out, that even in glomerular filtration a change in the 

 salt content of the filtrate from the blood may occur, since salts and 

 water are not taken up equally during swelling (see p. 69). We can 

 thus more readily understand how a salt solution hypotonic towards 

 blood may flow from the glomeruli, although according to R. BURIAN 

 an isotonic filtrate is always obtained upon ultrafiltration through an 

 artificial ultrafilter. Moreover, the difference in the reaction of 

 blood and of glomerular filtrate may contribute to the dilution. 



R. A. GESELL made a remarkable observation. Repeating BECH- 

 HOLD'S experiment he employed more rapid pulsation and lower 

 pressure and obtained from defibrinated dog's blood a filtrate richer 

 in globulin with the steady than with the pulsating pressure. 



Obviously, the glomerular membrane is just at the limit of permea- 

 bility for serum albumin; albumoses pass over into the urine. We do 

 not know whether the normal urinary colloids such as urochrome are 

 derived from the glomeruli or secondarily from the urinary tubules. 



This explanation receives valuable support from the investigation 

 of MARTIN H. FISCHER.* As we saw on page 215 et seq., there is in 

 the body a dynamic swelling equilibrium for the organ colloids which 

 may be regarded as constant for a brief period in thirsting individ- 

 uals; in them the secretion reaches a minimum. With excessive 

 ingestion of water, edema does not by any means occur, but the excess 

 of water is excreted by the excretory glands, especially the kidneys. 

 As we have seen on page 220, there is a very narrow range of swelling 

 for the blood; as the result of this all water (free water in contrast 

 to water of swelling) which is in excess of what is needed for the normal 

 condition of hydration of the blood is filtered off by the kidneys, 

 especially if the muscles, the main reservoir, are already saturated 

 with water. A most convincing proof that it is not the absolute 

 quantity of water but the swollen condition of the blood colloids 

 which is of significance for the secretion of urine may be found in 

 the older experiments of E. PONFICK and the more recent ones of R. 

 MAGNUS.* 1 These investigators transfused a rabbit with the blood 

 of another rabbit so that its blood was increased from 30 to 70 per cent. 

 In spite of this there was no increase or hardly any increase in the 

 excretion of urine. The same results were obtained for dogs and rats. 



The novel conception introduced by M. H. FISCHER * is the fol- 

 lowing: blood rich in C0 2 (venous) has a tendency to swell, or absorb 

 water; blood poor in C0 2 (arterial) has a tendency to shrink or give 

 up water. The blood passing to the intestines is very rich in CO2 



