FILTRATION. 



283 



On the other hand, the older experiments of Schmidt l with gum 

 and albumin gave quite opposite results ; thus (p. 364 of 1861 paper) 



Albumin through Ox Pericardium. 



And the experiments of Gottwalt 2 and v. Kegeczy 3 are in agreement 

 with those of Schmidt. 



According to Lowy, 4 who filtered serum and egg albumin solutions 

 through pig's bladder at constant pressure, rise of temperature affects 

 the quantity of the organic solids filtering more than the inorganic, and 

 such slight temperature changes as from 37'5 to 41 0- 5 C. have a distinct 

 effect. 



It is therefore evident that our knowledge of the phenomena of filtra- 

 tion through animal membranes is at present very restricted, and it is 

 of course impossible to directly apply the results of the above observers 

 to filtrations in the living body. No experiments, perhaps, have more 

 clearly pointed out the difference between a dead and living filter than 

 those of Tigerstedt and Santesson 5 with the frog's lung. A fresh frog's 

 lung, filled with -6 per cent, sodic chloride solution, will stand a pressure 

 of some 13 or 14 mm. of mercury without filtering for many hours ; 

 heating in water at 54 C., or treatment with weak acetic acid, frog's bile, 

 weak sodic hydrate, or distilled water, at once, however (presumably by 

 killing the cells), allows filtration. Leber, 6 moreover, showed that the 

 fresh cornea, provided the epithelium of the membrane of Descemet is 

 intact, will stand a pressure of 200 mm. of mercury, but at once 

 allows filtration to occur when the epithelium is removed, the tissue 

 of the cornea itself allowing fluid to pass. 



It must be confessed that experiments on living membranes (and 

 these alone) can give any information of real value ; and, furthermore, it 

 must be remembered that filtrations in the body are, as a rule, accom- 

 panied by osmotic phenomena, since filtration must nearly always occur 

 from one solution into another, and not into air, as in most experiments. 



In concluding this article, a word must be said with regard to the 

 theory that in some cases the cells of a part take some active part in 

 moving solutions across membranes. So little is known of cell mechanics, 

 that if such a process does take place we have certainly no conception 

 of its modus operandi, and it is at least probable that a process con- 

 sidered to-day as a " vital action " may in the future become capable 

 of a simpler explanation. Certainly, if the same solution is placed on 



1 Loc. cit. 2 Loc. cit. 3 Loc. cit. 4 Loc. cit. 



6 Arch.f. Ophth., Leipzig, 1873, Bd. xix. Abth. 2, S. 125. 



Loc. cit. 



