FOREWORD: Visible biological radiations have always greatly attracted mans curiosity fireflies and glow worms, I uniiiit went wood, phosphorescent meat, and the illuminating organs of deep sea fish are among the well-known wonders of nature. The biological importance of this luminescence seems to be in no proportion to the impression it makes upon the human mind. While it is assumed by some biologists that it has the purpose of attracting the prey, of frightening enemies, or of luring the male to the female, other investigators have contested these theories. The phosphorescent bacteria usually lose the ability to produce light when cultivated for some time on artificial media, without any apparent decrease in vitality. The emission of visible light is probably of no greater importance than color it plays no essential role in the cell physio logy of the organisms. Quite to the contrary, the invisible radiations of living org anisms are of considerable physiological significance. They play a distinct part in cell division and in growth. They are evident ill the healing of wounds. Old age is accompanied by complete cessation of ultraviolet emission perhaps this is the cause of old age. Beta-mdicitum controls the heart beat. The, loss of blood radiation is used in the diagnosis of cancer it may be that radia tion, or some disturbance of its mechanism, is Jinked with the. cause of cancer. Its role in the metamorphosis of amphibia has been demonstrated. Mutual influences of one species upon another by radiation have been observed. Biologists and physicists have always been suspicious of radiations from living organisms, perhaps only because the average man not to mention woman likes to believe in human radiations. However, the principal reason for the rejection of the discovery of ultraviolet emission from living cells was the inability of some to repeat the positive experiments of others with the same results. This had led to the fallacy that negative results disprove positive ones. It is quite evident that if two experimenters obtain different results, they cannot possibly iiave made the same experiment. Both results are correct, and the important task is to find out in what points the investigations differed. With a phenomenon so little understood as these biological radiations, it is not surprising that these apparent contradictions have not as yet been explained in every ease, though several factors responsible for negative results have been discovered. The objection to biological radiations has been strongest in this country, but even here, a more conciliatory attitude has be come noticeable since it has been shown that mitogonetic radiation is not a mysterious force, but the result of biochemical processes. Many simple chemical reactions have been found to emit weak ultraviolet rays. Another factor is responsible for the slow adoption of this new influence in biology practically all papers on this subject are published in foreign languages, and of the very few in English, almost all happen to contain negative results. This very fact has been one of the authors reasons for presenting the more important facts in this book...