- Dissolve gelatin in water according to directions.
- In a large bowl, mix dissolved gelatin with carrots, celery, cucumber, onion, lemon juice, and mayonnaise.
- Refrigerate for 25 hours.
- If the mixture becomes too jelled to spread well, add ⅓ to ½ cup more mayonnaise.
- Using an electric knife, trim crusts from bread edges.
- Spread vegetable mixture on bread and make 28 sandwiches.
- Cut into quarters.
- Layer cut sandwiches in a large covered plastic container with damp paper towels between layers until serving time.