50 



MACDOUGAL^ACTION OF LIPOIDS IN GROWTH. 



Another series of slices of Opimtia about 2.5 mm. in thickness 

 Were first allowed to hydrate in water for 6 hours, in which time an 

 increase of 35 to 40 per cent, was noted. The water in the dishes 

 was nov/ pipetted ofif and replaced with other solutions. Saponin 

 0.005M and a mixture of saponin 0.005 ^^^ KCl 0.005M resulted in 

 a rapid shrinkage to about the original dimensions in 10 hours. KCl 

 o.oosM had no effect on a trio of sections which quickly shrtmk when 

 the salt was replaced with saponin 0.005M. 



The maximum swelling of thin sections of dried material of 

 Opimtia was reached at a concentration of saponin between o.ooiTkf 

 and 0.005M. Samples which swelled 150 per cent, in water made 

 an increase of 188 to 200 per cent, in such saponin solutions. Other 

 samples which swelled 220 per cent, in water showed increases of 

 260 to 320 per cent, in saponin at the above concentrations. The 

 increase was practically identical with that of water at 0.0002M and 

 at o.oiM and stronger. The sections first dried and then hydrated 

 as above showed no shrinkage at the end of 36 hours, even in the 

 stronger solutions. The action seems to be one purely of imbibition 

 of water by walls, mucilages, and lipoids. It is not affected by KCl. 



The hydration of living sections in saponin shows the effect of 

 altered permeability. A series of thin slices of living tissue were 

 hydrated in a graded series as below, and after full expansion had 

 been reached a neutral salt, NaCl, was added to increase permeability 

 in some sections. The results are given below : 



The initial swelling of the sections is met and canceled most 

 quickly in the stronger solutions, which increase the permeability of 



