The scientist Dame Julia Polak, who has died aged 75, was a leading figure in the field of histochemistry, the study of chemical components in cells and tissue. After receiving a heart and lung transplant in her mid-50s, she embarked on a remarkable second career developing laboratory organs for transplantation.
As a histochemist, Julia pioneered the use of a technique known as immunohistochemistry to make peptides amino acid compounds visible under a microscope. It is now routinely used in labs all over the world. She was able to show that peptides were located within nerves; a highly original finding. She further demonstrated that these peptides were actually present in the little granules that the nerves release when they are activated and by which they control other tissues. This meant that nerves talk to each other by means of peptides. While she first found this in the gut, bladder, lung and heart, she later showed it was also true of the brain itself.
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