Obituary: Norman Pirie

Norman Pirie was a biochemist distinguished for his pioneering work on plant viruses, a crusading advocate for the dietary use of leaf protein and, more broadly, a man of science who wrote with force and lucidity on many scientific questions of his time.

"Bill" Pirie was the third and youngest child of Sir George Pirie, the animal painter, and spent his early years in Torrance, Stirlingshire. The family lived in a large isolated house with enough space for all of them to pursue their own interests. Pirie's early schooling was disrupted for a number of reasons, including the development of a stammer. He maintained that this disruption allowed him more time in the lively, active atmosphere of his family and greatly benefited his intellectual development. From this upbringing he derived a strong sense of independence, self-reliance and frugality and a lifelong love of language and etymology.

At Cambridge (Emmanuel College) Pirie discovered biochemistry, and blossomed in the creative atmosphere of the department of Sir Gowland Hopkins. On graduation Hopkins appointed him demonstrator, and his early research work was on glutathione and sulphur metabolism. He collaborated with Ashley Miles on the antigens of the pathogenic bacteria Brucella abortus, but of greater importance was his meeting Fred Bawden, who interested him in the problem of isolating the viruses responsible for causing diseases of potato. This was the beginning of 38 years of close friendship and collaboration that only ended with Bawden's death in 1972.

The collaboration continued following their move to Rothamsted Experimental Station in Harpenden, Bawden moving there in 1936 and Pirie in 1940. Here the scope of their work was extended and they accomplished the separation in semi-crystalline or crystalline form of 12 or more viruses or strains of viruses, including tobacco mosaic virus (TMV), and showed that they all contain nucleic acid of the type now called RNA, the genetic material of viruses. This was work of a high technical standard, and was, moreover, in a competitive area. Others, including W.M. Stanley, had previously claimed to have isolated TMV and made great reputations; but their preparations had few of the properties that we accept for TMV today.

If chance played any part in Pirie and Bawden's discovery of viral RNA, we must remember Pasteur's dictum that "chance favours only a prepared mind". Both Pirie and Bawden had prepared minds. They were sceptical of the then current concepts of "purity" when applied to large molecules, and sceptical too of the dominant emphasis on proteins. They were prepared to look for other components in virus preparations and acknowledge their possible importance. They realised that viral RNA might carry virus activity and tested this possibility. For technical reasons the results were negative, and it was left until 1956 for others to establish the infectivity of RNA.

Pirie's mind was also well prepared for the striking semi-crystalline nature of concentrated suspensions of TMV. He delighted in the coloured sheens that appeared when the opalescent suspensions were swirled in a flask and viewed by polarised light. He correctly interpreted this streaming birefringence as the property of rod-like particles and used it to estimate their size. With characteristic flair, the birefringence was demonstrated at a Royal Society soiree when dilute suspensions of TMV were stirred by goldfish and sea horses. Pirie joked that, initially, suspensions of TMV were as popular with fish physiologists as with plant pathologists.

By the 1950s Pirie's interest shifted and he had begun his ardent campaign to promote extracted leaf protein as a beneficial and cheap human food. This work had begun with government encouragement during the early days of the Second World War, when there was concern over food resources. Pirie recognised the potential of leaf proteins which are indigestible in intact leaves and are only very inefficiently converted to edible forms by herbivores.

After the war the project developed to encompass the nutrition of the world's increasing population. With a small team of engineers, chemists, nutritionists and cooks, Pirie developed a variety of machines to disrupt suitable leaves, press the juice out of the fibre and steam-precipitate its proteins. Perhaps the most useful of these "mechanical cows" were the smaller "village units" that were designed to be used by rural communities with limited technical resources.

With the help of charities, these units were exported to many less developed countries. Getting them installed and functional, and getting the green product incorporated into acceptable food, proved difficult, and involved social and political problems and prejudices. Although the nutritional value of the protein concentrates has been amply demonstrated in India and elsewhere, the project has not taken off in the way Pirie hoped and expected. The reasons are complex and it may partly be because the world protein deficit predicted during the 1950s has not materialised as expected. Nevertheless the project continues and it may well yet become needed; if and when it does, Pirie will have provided its necessary theoretical infrastructure.

Since his formal retirement Pirie studied beta-carotene, or pro-vitamin A content of his leaf extracts and became convinced that in the present circumstances, this was more important than its protein. The dietary deficiency of pro-vitamin A affects many hundreds of thousands of people worldwide, resulting in much preventable blindness. This situation was well known to Antoinette (Tony) Pirie, Pirie's late wife, who as an internationally distinguished eye-biochemist monitored and crusaded against it. Pirie observed that the beta-carotene of his preparations was unstable, and tried to understand the destructive mechanisms and to prevent them. This work was financed by the shrewd investment of the Rank Prize for Nutrition and Agronomy with which he was presented in 1976.

Besides these main research subjects, Pirie published on a wide range of subjects, including the origin of life, the biology of space travel, the history of science, contraception and the dangers of nuclear weapons. There are as yet undeveloped patents on chemical contraceptives held partly in his name, so that he could claim to have worked on both sides of the population problem - population growth and its nutrition. His views on the origin of life were characteristically individual and he was sceptical of those who sought its origin in nucleic acid-like compounds produced in the "primeval soup" of the prebiotic earth. Forty years ago Pirie's friend J.D. Bernal, the distinguished physicist, wrote a book on this subject. Pirie was unimpressed, and in a forthright review, he sternly instructed Bernal to emulate the cobbler and "stick to his last".

More generously, he conceded that Bernal would need as many arms as the mythical giant Briareus to attend adequately to all the lasts on which he was qualified to bang. In thus describing Bernal, Bill Pirie might well have been describing himself.Norman Wingate Pirie, biochemist: born Torrance, Stirlingshire 1 July 1907; Demonstrator, Biochemical Laboratory, Cambridge 1932-40; Virus Physiologist, Rothamsted Experimental Station 1940-46, Head of Biochemistry Department 1947-73; FRS 1949; married 1931 Antoinette Patey (died 1991; one son; and one daughter); died Harpenden, Hertfordshire 29 March 1997.