Possible Clues:

• A stubborn worker seen around river vessel
• A drug conveyer with petty officer in a small vessel
• A flower put in shoe, medicine in it
• Glass container for hypodermic dose
• Vessel holding liquid for injection
• Capsule containing injection dose
• One gets shot of what's in it
• Glass capsule
• Capsule big enough to get Oxford University inside
• Water, say, at bottom of a minute glass container