Bring the chicken stock to the boil in a pan. Meanwhile stand the corn on the cob on a board and slice away the kernels with a large sharp knife. Add the corn to the stock and simmer away for 5 minutes.
Check over the crab meat for any little pieces of shell, keeping the meat in the largest pieces possible. Mix the cornflour to a paste with a little cold water, stir into the soup and simmer for 2 minutes.
Stir in the crabmeat, ginger, spring onions, soy sauce, rice wine or sherry and season to taste with salt and pepper. Simmer for 1 minute.
Now give the soup a good stir, remove the spoon and trickle in the egg white, so that it forms long thin strands in the soup. Simmer for about 30 seconds and then serve immediately.