27 In seems beyond argument that when a person suffers an injury, as a result of the negligent act or omission by a second person and subsequently the act of a third person also harms the plaintiff, that the actions of the second and the third persons are regarded as different in law, that is, such actions cannot be regarded as being a "joint" or "concurrent" tort, but the second tort is regarded as a subsequent tort. The respondent argued that the damage is not the "same damage" in each case: see Dillingham Constructions Pty Limited v Steel Mains Pty Limited (1975) 132 CLR 323 especially at 326-7; Mahony v J Krusich (Demolitions) Pty Limited (1985) 156 CLR 522, 528-9. Mahony's case concerned the exacerbation of a work-related injury by the alleged negligence of a doctor. At the pages referred to in that case, the Court said:
"6. A negligent tortfeasor does not always avoid liability for the consequences of a plaintiff's subsequent injury, even if the subsequent injury is tortiously inflicted. It depends on whether or not the subsequent tort and its consequences are themselves properly to be regarded as foreseeable consequences of the first tortfeasor's negligence. A line marking the boundary of the damage for which a tortfeasor is liable in negligence may be drawn either because the relevant injury is not reasonably foreseeable or because the chain of causation is broken by a novus actus interveniens ( M'Kew v. Holland & Hannen & Cubitts (1970) SC(HL)20, at p 25). But it must be possible to draw such a line clearly before a liability for damage that would not have occurred but for the wrongful act or omission of a tortfeasor and that is reasonably foreseeable by him is treated as the result of a second tortfeasor's negligence alone: see Chapman v. Hearse (1961) 106 CLR 112 at pp 124-125. Whether such a line can and should be drawn is very much a matter of fact and degree (ibid., p.122). . .
7. In particular circumstances, minds may differ as to whether a subsequent injury was foreseeable or whether it is too remote to be regarded as a consequence for which an earlier tortfeasor may be held liable. When an injury is exacerbated by medical treatment, however, the exacerbation may easily be regarded as a foreseeable consequence for which the first tortfeasor is liable. Provided the plaintiff acts reasonably in seeking or accepting the treatment, negligence in the administration of the treatment need not be regarded as a novus actus interveniens which relieves the first tortfeasor of liability for the plaintiff's subsequent condition. The original injury can be regarded as carrying some risk that medical treatment might be negligently given: [ authorities cited] . It may be the very kind of thing which is likely to happen as a result of the first tortfeasor's negligence (cf. per Lord Reid in Dorset Yacht Co. v Home Office [1970] AC 1004, at p 1030). That approach is consistent with the view taken in workers' compensation cases that the total condition of a worker whose compensable injury is exacerbated by medical treatment, reasonably undertaken to alleviate that injury, is to be attributed to the accident: [ authorities cited] , although medical negligence or inefficiency can be held to amount to a new cause of incapacity in some circumstances: Rothwell v. Caverswall Stone Co . (1944) 2 All ER 350, at p 365; Hogan v. Bentinck Collieries (1949) 1 All ER 588, at p 592. In the last-mentioned case Lord Reid, in dissent, expressed the opinion that there is a break in the chain of causation when a doctor is guilty of such negligence as would make him liable in damages. We think, with respect, that that test is too rigid. Some degree of medical negligence in the treatment of an injury may well be a reasonably foreseeable result of the act or omission by which that injury was inflicted, and then no clear line can be drawn to limit the original tortfeasor's liability to exclude the consequences of medical negligence."