R v smith 1959- 2 sword men fighting, one injured, taken by medics, medical treatment aggravated the wound, v died. HELD- NO BREAK even though the medical treatment was bad, the operating cause was still the original injury. R v Jordan 1956 -v stabbed but healing well in hospital. v given antibiotics, allergic reaction, v died. HELD : BREAK the original injury not the operating factor. MA will not break chain unless its palpably wrong or extraordinary and unusual