. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . the grid was immersed in a solution of 3 g of a mixture of potassium permanganate and dichromate in concen- trated sulphuric acid for fifteen minutes. After removal, it was washed in water, then in concentrated hydro- chloric acid for a few seconds (this removed the manganese dioxide formed by the decomposition of the acid mixture), and finally in water. After drying, it was ready for shad- owing and examination in the electron microscope. Care must be exercised in the interpretation of electron micrographs of re
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . the grid was immersed in a solution of 3 g of a mixture of potassium permanganate and dichromate in concen- trated sulphuric acid for fifteen minutes. After removal, it was washed in water, then in concentrated hydro- chloric acid for a few seconds (this removed the manganese dioxide formed by the decomposition of the acid mixture), and finally in water. After drying, it was ready for shad- owing and examination in the electron microscope. Care must be exercised in the interpretation of electron micrographs of replicas produced by this technique, since a number of artifacts, which are easily recognisable, are liable to occur. The most obvious of these is distortion during the dehydration of the cell. This causes a very gross effect which can be clearly seen in figure 1. It is also likely that, in the case of large organisms such as yeast, the replica will become distorted and a similar effect produced. The rim at A in figure 2 is caused by cell dehydration and gives the appearance of the cell having been flattened against the formvar film. It was found that these artifacts were by no means a serious hindrance and undistorted cells could easily be found by systematic scanning of the grid. Two kinds of budding scar, illustrated in figure 1, were found on yeast cells. The "birth" scar (marked C), which is the scar formed at the point where a cell was attached to its parent, and the "bud"* scar (marked A and B), which is formed on the parent cell when the daughter becomes detached. These scars are quite different in form as can be seen from the figure. These observations are in agreement with those of Barton (2), who carried out his work opti- cally. The morphology of these scars is of great im- portance in a study of the mechanism of division. Electron micrographs of cells prior to division help in proposing a sequence of events for the process. Figure 2 shows the '&qu
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