And then, going back to the Coris who, of course, were the first pioneers in the study of glycogen... after I had left their laboratory and for reasons that had nothing to do with my being there, but, anyway, the latest interest of Gerty Cori, the wife of Carl, who shared the Nobel Prize with him... her major interest became the study of congenital glycogen storage diseases. These are a group... a set of diseases which are all inborn, congenital, genetic diseases in which, for one reason or another, glycogen accumulates in abnormal quantities in various types of cells. Therefore they are called glycogen storage disease. And so she studied the biochemical mechanisms that were involved in these diseases. She found one that was due to the absence of glucose 6-phosphatase, for instance. Another one was due to the absence of debranching enzyme and so on – several types – and among those different types she had described one called glycogenosis type II where she didn't find any abnormality that she could detect. When she died... I think it was probably in 1957; she died early. Carl lived much longer. She died of... I think it was aplastic anaemia or some rare blood disease. My friend and colleague, Hers, took over this job of studying biopsies from patients with different diseases and trying to find out... specially carbohydrate diseases, to find out by enzyme assays, what enzymes might be deficient or missing in those tissues. And so he became an expert on glycogen storage diseases and ran into a few samples of this glycogen storage disease type II which is also called Pompe's disease – it's the name of a Dutch paediatrician who described the first case sometime in the '30s – and, like Gerty, Hers was not able to find any deficiency in an enzyme involved in the known metabolism of glycogen. In fact, those children had no excuse for being sick because they would respond normally if you gave them glucagon or epinephrine – they would release glucose in their blood stream like anybody else – so there was no explanation for the storage of the glycogen, and Hers thought, well, an enzyme has been, not described, but postulated by, I think, Bill Whelan, probably, and maybe I should try and look for this enzyme in their diseased tissues. This was an enzyme assumed to be a transglycosylase, an enzyme that would transfer glycoside residues from maltose to glycogen, or from glycogen to maltose... whatever. And so he devised an assay for this hypothetical enzyme, which doesn't exist, actually, but in which radioactive maltose was used as a substrate, and he was expecting to find radioactivity in glycogen; and, in fact, he did not find radioactivity in glycogen but what he found was that there was in liver an enzyme that would split maltose... he called it maltase. And, by accident, having extended this kind of assay to a sample of a liver from a child afflicted with this disease, glycogen storage disease type II, found that this particular activity was missing.