On the Microscopic Methods of Measuring the Dimensions of the Bacterial Cell

It has been shown by the author (Knaysi, 1941) that the dimensions of cells measured on smears dried, fixed, and stained by the ordinary methods are con-siderably below those of cells in the living state and represent the dimensions of the shrunken protoplasm. More recently (Knaysi, 1944) the various methods of microscopic measurements were discussed, and it was concluded that values approaching true cell dimensions can be obtained either by measuring the living cells or in smears especially stained to show the cell wall. Measurements from electron micrographs were considered satisfactory when the cell wall is visible. It was also stated: "Figures obtained from negative smears are too high because they include also the slime layer usually surrounding the cell. In the case of capsulated organisms, the relative error may be tremendous. There is also an additional error due to the retraction, upon drying, of the coloredfilm inwhich the bacteria are imbedded." Working with Bacillus megatherium, Dubin and Sharp (1944) compared the dimensions of the same air-dried, unstained cells in photo and electron micro-