**Core Concept:** Local anaesthetics are medications used to temporarily block the transmission of pain signals at the site of action, typically in the context of surgical procedures or dental treatments. They achieve this by inhibiting voltage-gated sodium channels in neurons, preventing the generation and conduction of action potentials.

**Why the Correct Answer is Right:** The correct answer, "**B. Procaine**," is the first local anaesthetic to be used clinically. Procaine is a local anaesthetic agent that belongs to the class of amide local anaesthetics. It was introduced in 1905 and has been widely used for its effectiveness in providing temporary analgesia.

**Why Each Wrong Option is Incorrect:**

A. **Lidocaine**: While lidocaine is also a local anaesthetic amide agent, it was developed after procaine, making it incorrect as the first choice. Lidocaine was introduced in 1948.

C. **Benzocaine**: Benzocaine is an ester local anaesthetic, not an amide as procaine and lidocaine are. It was introduced in 1927 but is not considered as the first local anaesthetic agent.

D. **Morphine**: Morphine is an opioid analgesic, not a local anaesthetic. It was introduced in 1805, which is earlier than procaine, but it is unrelated to the concept of local anaesthesia.

**Clinical Pearl:** Procaine, despite being introduced later than lidocaine, remains in use due to its favorable pharmacokinetic properties, such as rapid onset and shorter duration of action, which makes it suitable for certain clinical situations where a rapid onset and short duration are desired.

**Correct Answer:** Procaine (B) was the first local anaesthetic to be introduced clinically. It belongs to the class of amide local anaesthetics, which includes lidocaine and bupivacaine, and was developed in 1905 by Adolf Neuberg.