1905.] Crystalloids and Colloids through Gelatine. 313 



containing excess of antilysin, by the author;* the filtrates showed no 

 hsemolytic power, whereas the gelatine had stored up a considerable amount 

 of free megatherium lysin. In this light Martin and Cherry's observations 

 on diphtheria toxin and snake venom, mentioned above, are in entire agree- 

 ment with my results for megatherium lysin, the free toxin and venom of 

 the neutral mixtures being probably stored up in the gelatine of their filters. 



On " Wet" and "Dry" Gelatine Filters. — Martin and others used the 

 filters in the " wet " state, i.e., shortly after solidification of the gelatine 

 in the pores of the candle, and, therefore, containing a considerable quantity 

 of water, part of which on filtration will pass into the filtrate and so dilute 

 the substance filtered. To get rid of this difficulty, E. W. Eeid removed 

 part of the water by drying Martin candles to constant weight in a current 

 •of dry air. It seemed to me, however, that by drying the gelatine another 

 difficulty might be introduced, viz., a change in the size of the pores, which 

 would render observations with " dry " filters of doubtful value. 



Method. — The rate of filtration of water through freshly prepared wet 

 filters was observed during one hour and compared with the rates during a 

 similar period, of filters which had been partially dried by standing in dry 

 air for 10 hours, 24 hours, and 3 days. 



Bates of Filtration. — The freshly prepared wet filters gave fairly uniform 

 rates, and allowed from 0*5 to 2 c.c. of water to pass per minute at 

 100 atmospheres pressure, the concentration of the gelatine in the pores 

 being 9 per cent, and the temperature 10° to 15° C. Under the same 

 conditions the partially dried filters allowed from 5 to 20 c.c. to pass per 

 minute at the beginning of the filtration, but the rate rapidly decreased. 

 On reducing the applied pressure to about one atmosphere, and allowing 

 the water to flow through a partially dried filter at the rate of about 

 1 to 2 c.c. per minute, the filter gradually tightened, so much that after 

 the passage of 30 to 50 c.c. a pressure of 100 atmospheres was necessary to 

 maintain the same rate. The longer the filters were dried the more marked 

 •was the porosity and the greater the amount of fluid which had to be pressed 

 through before the filter tightened. 



Conclusions. — On partially drying gelatine filters the gelatine shrinks, 

 and air passages are produced of greater diameter than the water passages 

 of a wet filter. The wide dry filter passages at first offer a free passage to 

 the fluid filtered, and no material change is to be expected in the percentage 

 composition of the latter. The filter gradually changes in character until 

 ultimately, a wet filter is obtained with pores of similar dimensions to those 

 •of a freshly prepared wet filter. The various fractions of filtrate from a 



* Loc. cit. 



2 A 2 



