And so, a year later, another patient with the disease was detected at the University of Brussels and Pierre Baudhuin in our laboratory did a microscopic... electron microscopic examination on the biopsy fragment of the liver of that child because, by that time, we had acquired an electron microscope and Baudhuin and Beaufay were the main experts and so they found that, indeed, the glycogen, or much of the glycogen in this pathological sample, was surrounded by a membrane, was confined within a sac-like particle which, presumably, was a lysosome, and this indeed turned out to be the case. And so, in this way, he discovered the first lysosomal storage disease which he then went on to generalise into a major concept, the concept of an inborn lysosomal disease being that in the cells all kinds of materials – lipids, polysaccharides, you name it, they are there – get into lysosomes, sometimes by endocytosis but most of the time by autophagy. Those materials are then digested in the lysosomes by... 50 or more enzymes are now known... broken down... the products of the breakdown... the breakdown products go through the membrane, are utilised by the cell, and this goes on and on and on. But if one of those enzymes happens to be missing or deficient then among all this material, those molecules that require the missing enzyme to be broken down, would accumulate. And so, depending on the nature of the missing enzyme, you would have a different kind of chemical material accumulating, always in the lysosomes. Now, that was a tremendously fruitful concept – it was a paper published in Gastroenterology in 1965 –and it has a major impact on the whole field because, for a number of... many years the whole category of diseases was known; they were called storage diseases, they were genetic diseases – in French they were called thesaurismoses... thesaurismosis, essentially due to their abnormal storage of materials within cells, and those could be mucopolysaccharides of one form or another... in Hurler or Hunter Disease, could be lipids of one form or another; or another, glucocerebrosides, glycolipids, in Gaucher's Disease, in Fabry's Disease; sphingomyelin in Niemann-Pick Disease. I mean, these diseases all have the names of the physicians who described them but there was a whole mysterious chapter of pathology and literally, from one day to the other, the whole thing was clarified. Of course it needed many investigations by a number of really very good biochemists, mostly in the United States, to actually identify the missing enzyme and... clarifying the whole field. So that was a major... a major contribution which interestingly was made through the lysosome field by the only one in my group who had actually decided he didn't want to have anything to do with them, but that's life.