What a great gadget, the Dr Eves Stomach Pump, retailed by Farlows & Co in the last 1930's
With this device, you could extract the contents of the freshly caught Trout and Grayling to examine its food and exactly match the hatch.
With a small magnifying glass to examine fully the contents of your catch.
Never seen one before but this example is boxed, mint and unused. Maxtone-Graham details this in his book, Fishing Tackle of Yesterday.