Wouter Basson.
Stellenbosch University Professor Gert Jacobus Muller on Monday gave evidence on toxic chemicals and poisons, including those used in warfare.
"A toxic chemical means any chemical that, through its chemical action on life processes, can cause death, temporary incapacitation or permanent harm to humans or animals," Muller told the court.
"This includes all chemicals, regardless of their origin or of their method of production. It is a dose which determines whether a chemical is a poison or not. If you take in 250g of table salt in one shot it is probably potentially lethal."
He said even water could cause intoxication. He gave the categories of chemicals, including irritants used in teargas and their effects.
Basson's lawyer, Jaap Cilliers, led Muller in giving his evidence in chief.
Earlier, Muller told the Health Professions Council of South Africa committee chairing the hearing he was a medical practitioner for 45 years.
He worked in South Africa and England, and wrote various medical journals and books.
Muller's heart attack
The hearing was postponed in December 2012 because Muller had a heart attack two weeks before he was due to take the witness stand.
At the time, Cilliers handed in a medical certificate from Muller's cardiologist stating that he was not allowed to travel by air and would not be able to testify.
Another Basson witness, former surgeon general Dr Niel Knobel, is recuperating from open-heart surgery.
Basson is accused of acting unethically by being involved in the large-scale production of Mandrax, cocaine and teargas, of "weaponising" teargas and of supplying it to Angola's Unita leader Jonas Savimbi.
He is also accused of acting unethically by providing disorientating substances for cross-border kidnappings, and by making cyanide capsules for operatives to use to commit suicide in case of capture.
Basson violated laws of humanity
United States medical ethics expert Steven Miles previously testified that Basson violated the laws of humanity and various World Medical Association declarations and regulations.
In contrast, Knobel said Basson was a soldier and not a doctor when he headed the country's chemical and biological warfare programme.
Knobel disagreed with Miles's view, that once someone was a doctor they remained a doctor and that Basson made use of his medical knowledge and skills when he headed the programme.
Basson argued the surgeon general at the time was in charge of the programme and that he carried out orders as a soldier. – Sapa