Why does the human blood not clot in the alimentary canal of leech?

Explanation

### Step-by-Step Solution:

1. **Understanding the Leech's Feeding Mechanism**: Leeches are blood-feeding parasites that attach to their host and draw blood. When they do this, they need to ensure that the blood remains in a liquid state to facilitate easy feeding.

2. **Role of Saliva in Blood Feeding**: The saliva of leeches contains a specific enzyme called hirudin. This enzyme plays a crucial role in preventing blood from clotting while the leech is feeding.

3. **Function of Hirudin**: Hirudin acts as an anti-clotting agent. It inhibits the normal clotting process of blood, allowing the leech to consume the blood without it coagulating. This ensures a continuous flow of blood into the leech's body.

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