68 CARNEGIE INSTITUTION OF WASHINGTON. 



straight or curved lines. The sharp intercellular boundaries can be seen 

 in the living cultures as well as after iodine fixation or silver-nitrate treat- 

 ment. There may, however, be some overlapping of the cell edges. At the 

 periphery of the membrane transitional cells, varying from mesenchyme to 

 mesothelium, are found. As the cultures become older the mesothelial 

 membranes may loosen up into reticular cells, which finally contract into 

 more or less globular forms. The mesothelial cells on fixation often exhibit 

 distinctly marked fibrils extending to the periphery of the cell. These appear 

 to be coagulation fibrils, similar to those in fixed endothelial cells. The 

 observation of this transformation of mesenchyme into mesothelium provides 

 the embryologist with an explanation for many developmental phenomena 

 not heretofore clearly understood. 



Viability op Cells. 



Dr. W. H. Lewis and Dr. C. C. McCoy, using new criteria of death, have 

 determined the period of survival of the different types of cells and under 

 various conditions after the death of the animal. Experience with tissue- 

 culture has shown that all types of living cells either have or can develop 

 granules and vacuoles which possess a marked affinity for neutral red. In 

 the ordinary strengths this dye does not stain the cytoplasm or nucleus, 

 nor does it seem to injure the cell. In dead cells, however, the granules 

 and vacuoles do not take up the neutral red as they do in living cells, but 

 the dye, if it be strong enough, stains the whole cell diffusely. Granules and 

 vacuoles that have been colored with neutral red lose their color when the 

 cell dies and the whole cell becomes more or less diffusely pink. In addition 

 to this specific reaction to neutral red, there are definite changes in the texture 

 of the cytoplasm and nucleus that are discernible in dead cells, and the 

 nuclear membrane becomes more marked. Tissue-cultures have shown that 

 most cells not only survive, but move about and multiply for many days 

 after removal from the body, and it is well known that epithelial cells have 

 been cultivated for months, and connective-tissue cells may live and multiply 

 for years if given the proper environment. Under ordinary circumstances, 

 however, at the death of the animal all the cells of the body are subject to great 

 functional disturbances. With the cessation of heart action all the tissues 

 are immediately deprived of their chief source of oxygen, their food-supply, 

 and the pathway for the elimination of their waste products. Since the 

 various types of cells differ from each other in their chemical and physical 

 constitution, in the rate of metabolism, in the amount of oxygen, various 

 salts and foodstuffs used, and in the chemical composition of their waste 

 products, it is clear that they will react differently when the animal dies and 

 their environment changes. The period of survival depends on how well each 

 type of cell is naturally fitted to live under the abnormal conditions. In 

 order to test these factors and thus obtain further knowledge of the make-up 

 of different cells, Dr. Lewis and Dr. McCoy carried out experiments the 

 results of which are shown in the accompanying table. Regarding the inter- 

 esting problem as to the nature of granules and vacuoles, their observations 

 tend to show that these are waste products of autolytic or self-digestive 

 processes, and that their affinity for neutral red is a coincidence. 



The following table shows how long various cells of the body survive, 

 under different conditions, after death of the animal (rat). The cells were 



