The evidence shows that leukaemia is an incurable disease. It is a malignant disease of the blood, marked by an abnormal - because unregulated or autonomous - proliferation of cells. According to the type of cell affected it is classified as myeloid or lymphatic. It may be said to be, in a general sense, a form of cancer, and it is sometimes described as cancer of the blood. The aetiology of the disease is not known. But one of the witnesses called for the plaintiff, Doctor B. G. Haines, on being told of the events that had happened, stated that in his opinion there was a causal relationship between the injuries that the deceased man had suffered and the onset of the malady. Doctor Haines is a graduate in medicine of the University of Sydney and a member of the Royal College of Physicians. He is an assistant honorary physician at a large public hospital, and he practises as a consulting physician. Asked to justify his opinion, he propounded a theory that he said was based upon his own consideration of the topic. Briefly stated, his view is that emotional disturbances, operating in conjunction with other things, can be a factor in producing leukaemia, and he said all forms of cancer. Under cross-examination he went still further and, without qualification or restraint, asserted as his opinion that mental states and emotional disturbances are the cause of all, or nearly all, diseases except those of infective origin. He agreed that this was not an accepted view, and indeed that it had, as yet, no positive adherents other than himself: but he said that medical science was coming steadily more and more to this idea and that he expected that it would in time receive general recognition. He did not say that emotional factors were sufficient in themselves to account for all forms of leukaemia: they operated only in conjunction with other things; but, other factors being present, emotional disturbance could be decisive in producing the disease. So far as he was allowed to expound the basis for his opinion and to explain the nervous and physiological mechanisims that he considered were involved in it, it seemed to depend upon the functioning of the hypothalamus and derangements of its functions. Answering a cross-examiner is not, however, a satisfactory method for the complete exposition of theories of cyto-pathology. And the purpose of the cross-examination here was not really to enable him to explain his doctrine, but rather to discredit it in the eyes of the jury by getting him, without allowing any opportunity for qualification or elaboration, to give categorical answers that it was hoped would appear so extravagant that his evidence might be scoffed at. He did make assertions that to many people must appear in a high degree improbable. And the physicians called for the defendants did not accept his theory. But, however far-fetched some of his statements may seem, however much his theory may be criticized as unproven, however much it is out of line with orthodox opinion, it would be a bold court that could say that he was not qualified to express an opinion on medical matters and that the jury should have been told that, as a matter of law, they must disregard his opinion. The learned trial judge did in effect advise them to treat it with scepticism. Doctor Haines said he had reached his general conclusion as a result of consideration that he had for years given to the influence of psychological factors in producing physical disorders. He had published a small book on psychosomatic medicine under the title "Autonomic Dyspraxia". He had not at that time expressly included leukaemia as coming within the scope of his theory or system. He said, however, that subsequent consideration had led him to think that it too should be included within its range.