The basophllic material in the base of the pancreatic cell was named ergastoplasm by Gamier (21) because of its close association with the synthetic activity of the cell. Observations by Caspersson (10), Brachet (7), and others (13,24,25) have provided strong evidence that cytoplasmic nucleoproteins, the basophilic substances of the ergastoplasm, participate in the synthesis of proteins. The morphological and chemical details of the relationship between ergastoplasm and protein synthesis have remained obscure, however, in part because of the low resolving power of the ordinary microscope and in part because protein synthesis in ~/tro has not been accomplished. With the increased resolution of the electron microscope it should be possible to reexamine the relationships between the ergastoplasm and protein synthesis.These relationships have been studied in the exocrine portion of the pancreas of Swiss albino mice. Mice were fasted, and their pancreatic cells thus depleted of ergastoplasm and secretion granules. The animals were subsequently fed, and the formation of these elements was traced in detail. Observations made in the course of these and ancillary experiments indicate that the ergastoplasm is composed of sacs of variable structure, the membranous walls of which contain ribonucleic acid. New ergastoplasmic sacs appear mainly within cytoplasmic centers and also, but much less frequently, in apposition to the nuclear membrane, and possibly in relation to the basal plasma membrane. Small ergastoplasmic sacs, at first apparently empty, later accumulate material within their lumens, and become transformed into the well known secretion granules. Materials and MetkodsTen to 20 week-old Swiss albino mice were used in all the experiments. The animals were killed by decapitation, and a sm~|l piece of pancreas was obtained within 2 minutes of the

Biscossi (1) and later Cramer and Ludford (2) beautifully illustrated their contention that the Golgi complex plays an important role in fat absorption by intestinal cells. Unfortunately, their clear observations have been obscured by the controversy which has raged over the structure, and indeed the very existence of this organelle. Electron microscopy has clarified the confusion regarding the Golgi complex (3, 5, 15), demonstrating both its existence and its main structural features. Taking advantage of this technique, we have reinvestigated the process of fat absorption, and have confirmed the earlier observations, succinctly stated by Cramer and Ludford, that " . . . d u r i n g fat absorption, the Golgi apparatus is the cell structure mainly concerned." Materials and MtthodsEight to ten week old male Swiss albino mice were used in this study. The animals were killed by decapitation. A 2 to 3 ram. segment of the second centimeter of the duodenum was removed within 1 minute of the time of death, opened by a longutudinal slit, and placed into a small amount of the pH 7.2 osmic add-dichromate fixative recently devised by Dalton (4). After fixing for 1 hour, the tissue was washed for a total of 30 minutes using six changes of tap water, and then dehydrated by successive transfers lasting 10 minutes each through three changes of 95 per cent ethanol and three changes of absolute ethanol. The tissue was next transferred to a half-and-half mixture of absolute ethanol and methacrylate. The methacrylate was composed of three parts n-butyl methacrylate to one part methyl methacrylate. After three changes of methacrylate the tissue was embedded in methacrylate to which the catalyst, benzoyl peroxide, had been added. Polymerization was carried out at 37°C. for 24 hours. Sections were cut with a Minot microtome modified as described by Dempsey and Lansing (6) and equipped with a glass knife. The sections were examined without removing the plastic in an RCA model EMU2E microscope with a 40 tt aperture in the objective lense. Eiectron micrographs were taken at an original magnification of from 1,000 to 10,000 times and enlarged photographically as desired.The fine structure of duodenal cells from control and fat-fed animals was studied. Control mice received regular Purina lab chow and water ad lib. In the fat-feeding experiment seven mice were deprived of food and water for a 24 hour period, starting at 6 a.m. At 6 p.m. on

Mitochondrm are important in ion transport, as has been shown in recent biochemical studies. For e~ample, Stanbury and Mudge have shown that isolated mitochondria are capable of maintaining high concentrations of potassium when suspended in potassium poor solutions (7), and Bartley and Davies have shown that isolated mitochondria can take up cations from the surrounding solution against a concentration gradient (1).Mitochondria concentrate the cationic dye Janus green, as is well known from light microscopic observations. That the cationic dye neutral red is also concentrated by mitochondria has been shown by electron microscopic studies (10). This paper reports electron microscopic observations on the effect of sodium and potassium ions upon a cell normally engaged in their transport. The duodenal absorptive cell of the Swiss albino mouse was studied under varying salt and water loads. Mitochondfia were found to develop internal granules when these salts were administered in large amounts. Materials and MetkodsThe duodenal absorptive cells of Swiss albino mice were prepared and studied by the techniques described in the preceding paper. The adult mice were males, 8 to 10 weeks old.In order to assess the relative number of mitochondrial granules, at least ten high resolution micrographs were obtained for each animal. In questionable cases at least another fifteen micrographs were taken from another part of the duodenum. A total of 59 animals was studied.

Our experience with needle biopsy of the heart in dogs indicates that myocardial tissue can be sampled one or more times in each animal with comparative safety. Tamponade, pericarditis, serious arrhythmias, or myocardial infarction due to the interruption of coronary vessels was not observed. Excellent specimens were obtained for critical study by light and electron microscopy. Casten and Marsh (1) have used biochemical techniques to study myocardial tissue obtained in similar fashion. Histochemical methods would also be applicable. Although limited to animal studies at present, the technique may conceivably be adapted to the study of human disease. Myocardial puncture has been carried out (20–22) in patients for the recording of intracardiac pressures and for other diagnostic purposes without apparent harm. Our study of the myocardium of dogs by electron microscopy generally confirms the observations of other workers, except that presence of significant numbers of red blood cells in the extravascular spaces of the heart had not been previously described (and is possibly an artifact). Nevertheless, it is notable that the tissue cells, cellular membranes, and intracellular structures appeared to be intact and undistorted in the tissue specimens which were obtained, fixed, and examined by these methods.

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