Otto Warburg, Franz Wind, and Erwin Negelein discuss the metabolism of tumors in living animals, focusing on whether tumor cells can be killed through energy deficiency and how tumors are supplied with oxygen and glucose. They assume that tumor cells obtain energy through respiration and fermentation. Experiments on transplanted and spontaneous tumors show that both processes are active. Tumor cells can survive for a period using fermentation alone, but respiration alone is sufficient for their maintenance. Interfering with either process is not enough to kill tumor cells; both must be stopped to achieve energy deficiency and cell death. The authors explore the possibility of killing tumor cells in living animals by reducing energy supply. They find that while all cells require energy, tumors are more versatile in obtaining it compared to normal cells. However, tumors are less well-supplied with glucose and oxygen than normal tissues. The glucose content in tumor veins is significantly lower than in arteries, indicating poor supply. Lactic acid formation in tumors is confirmed, with veins containing more lactic acid than arteries, suggesting that lactic acid is produced as blood passes through the tumor. The authors estimate that 66% of glucose used by the tumor is converted to lactic acid, while the rest is used for respiration. This results in a significant loss of oxygen in the tumor blood. Fermentation is highly dependent on glucose concentration, and raising it can double tumor fermentation. However, merely reducing blood sugar levels is insufficient to kill tumor cells, as they can survive without glucose. Reducing oxygen levels, however, can effectively kill tumor cells, as demonstrated by experiments where tumor rats were exposed to low oxygen atmospheres. This effect is more pronounced than expected, suggesting that oxygen deprivation also affects capillary cells, leading to the death of both the arterial and venous tumor halves. The paradoxical nature of killing tumor cells through oxygen deficiency is explained by the fact that both yeast and tumor cells can be killed through lack of sugar for fermentation.Otto Warburg, Franz Wind, and Erwin Negelein discuss the metabolism of tumors in living animals, focusing on whether tumor cells can be killed through energy deficiency and how tumors are supplied with oxygen and glucose. They assume that tumor cells obtain energy through respiration and fermentation. Experiments on transplanted and spontaneous tumors show that both processes are active. Tumor cells can survive for a period using fermentation alone, but respiration alone is sufficient for their maintenance. Interfering with either process is not enough to kill tumor cells; both must be stopped to achieve energy deficiency and cell death. The authors explore the possibility of killing tumor cells in living animals by reducing energy supply. They find that while all cells require energy, tumors are more versatile in obtaining it compared to normal cells. However, tumors are less well-supplied with glucose and oxygen than normal tissues. The glucose content in tumor veins is significantly lower than in arteries, indicating poor supply. Lactic acid formation in tumors is confirmed, with veins containing more lactic acid than arteries, suggesting that lactic acid is produced as blood passes through the tumor. The authors estimate that 66% of glucose used by the tumor is converted to lactic acid, while the rest is used for respiration. This results in a significant loss of oxygen in the tumor blood. Fermentation is highly dependent on glucose concentration, and raising it can double tumor fermentation. However, merely reducing blood sugar levels is insufficient to kill tumor cells, as they can survive without glucose. Reducing oxygen levels, however, can effectively kill tumor cells, as demonstrated by experiments where tumor rats were exposed to low oxygen atmospheres. This effect is more pronounced than expected, suggesting that oxygen deprivation also affects capillary cells, leading to the death of both the arterial and venous tumor halves. The paradoxical nature of killing tumor cells through oxygen deficiency is explained by the fact that both yeast and tumor cells can be killed through lack of sugar for fermentation.