At the beginning of Chapter 10, Van Helsing provides Dr. Seward with the following allegory to justify his withholding of information on the true nature of Lucy's affliction:
'The good husbandman tell you [that the corn crop will be good] then because he knows, but not till then. But you do not find the good husbandman dig up his planted corn to see if he grow; that is for the children who play at husbandry, and not for those who take it as the work of their life. See you now, friend John? I have sown my corn, and Nature has her work to do in making it sprout; if he sprout at all, there's some promise; and I wait till the ear begins to swell.'
In this allegory, Van Helsing is the canny farmer, awaiting the "ripening of the corn" before asserting that the crop will be good. In Van Helsing's case, the corn is not literal corn but rather the events unfolding in front of him. In order for Van Helsing to prove with certainty to his friends that vampires abound and have preyed on young Lucy, he must first allow certain events to unfold. Without subsequent events as proof, his friends would surely not believe him, and would declare him mad. A wise man, Van Helsing waits for his cards to fall into place.
