RELATIONS OF BURSARIA TO FOOD 11 



which will confront us later regarding the absorption of the 

 liquefied products of digestion. 



Within one or two hours after the grain comes to lie in the 

 vacuole, the beginning of solution becomes apparent as a lique- 

 faction and consequent rounding off of the corners and, edges. 

 This proceeds in exactly the same manner as when cubes of 

 coagulated egg-albumen are digested by the action of pepsin- 

 hydrochloric acid. At the end of digestion no solid remains of 

 the vitellin grain can be seen ; all that is left is more or less liquid 

 in the vacuole. 



Another important visible change in the vacuole consists in 

 the usual second appearance of liquid about the vitellin grain. 

 It seems most in conformity with the observed facts to consider 

 this as a consequence of the formation of soluble products of 

 digestion, and as being due to the fact that the rate of resorption 

 of these liquid products is less than the rate at which the lique- 

 faction of the vitellin grain takes place. 



The reason for this conclusion is partly based upon the fact 

 that in some cases the whole process of digestion of the vitellin 

 may go on and be completed without the appearance of any 

 visible liquid between the grain undergoing solution, and the 

 vacuole membrane. In this case it is obvious that the rate or 

 power of resorption is equal to or greater than the rate of solu- 

 tion of the grain. Furthermore, it is to be expected that as 

 digestion of the protein continues, the affective osmotic con- 

 centration of the cleavage products increases and this obviously 

 may bring about an increase in the Uquid contents, provided that 

 the permeability of the vacuole membrane (resorption) does not 

 undergo a simultaneous, proportional increase. In other words, 

 the absence or presence of liquid during digestion of vitellin is a 

 resultant of two sets of conditions (a) the rate of digestion and 

 (b) the rate or power of resorption, one factor of which is the 

 degree of permeability of the vacuole membrane. This further 

 agrees with the fact that digestion of a vitellin grain is not always 

 at a uniform rate. A rapid solution of the grain sometimes 

 begins shortly after eating, changing later to a slower one. Even 



