Importance of controls for the demonstration of carbohydrates in electron microscopy with the silver methenamine or the thiocarbohydrazide‐silver proteinate methods

SUMMARY The periodic acid‐silver methenamine method and the periodic acid‐thio‐carbohydrazide‐silver proteinate method have been used for the demonstration of carbohydrates in various plant and animal tissues. The comparison of the results obtained with both methods indicates that the periodic acid‐thiocarbohydrazide‐silver proteinate method is more specific and gives better quality pictures than the PA‐silver methenamine method. It is pointed out that adequate controls are necessary for a valid cytochemical interpretation of the results. With the PA‐thiocarbohydrazide‐silver proteinate method, no positively stained structure can be assumed to be of carbohydrate nature unless it is found unstained in non‐oxidized thiocarbohydrazide‐silver proteinate treated sections. Both methods have their limitations and do not demonstrate the total carbohydrate amount in tissue sections.