Life cannot be defined as the sum of the attributes of living things. Nevertheless we may conceive that one attribute may be sufficiently constant to serve as the diagnostic sign of life. This is what Mr. Tashiro has demonstrated. "That mechanism," he says, "which enables living matter to respond to the external world . . . may be called the most characteristic thing in life. The chemical accompaniment, or basis, of this mechanism, discovered by the author in nerve fibers, he has hoped to show exists in all forms of living matter, both of plants and animals. It gives a chemical method of distinguishing living from dead tissue, and of measuring the quantity of life."
"A hundred years ago," Mr. Tashiro reminds us, "the electrical sign of life was discovered by Galvani, when he found that animal tissues are a source of electricity. ... It is now certain that whenever the response to a stimulus takes place in animals or plants—the response which is the sign of life—an electrical change accompanies it. . . . There is always and everywhere," he continues, "an accompanying chemical change of a particular kind which is as sure a sign of life and as invariable an accompaniment of the vital reaction as the electrical change. This chemical sign is the sudden outburst of carbon dioxide which all living things show—plants as well as animals, dry seeds as well as the nerve tissues of the highest mammals—when they are stimulated in any way."
Mr. Tashiro has devised a piece of apparatus called the biometer, which will detect infinitesimal amounts of carbon dioxide. The construction of the apparatus and the method of using it are fully described in the appendix. While we may imagine the high commercial value of being able to discriminate living from dead grain, to a psychologist perhaps the most interesting application of the biometer will be in the study of nerve action. "Whatever may be the nature of that activity going on in our minds," concludes Mr. Tashiro, "we have at least discovered something about its simplest chemical accompaniment. Perhaps the nerve impulse is something in the nature of a propagated explosive wave in a continuous substance. Whether that wave is in the nature of a hydrolysis or an oxidation we cannot say, but at any rate it results in the liberation, in some manner, of carbon dioxide. This substance tells us whether the nerve impulse has passed this way or not. The change which liberates it may be the impulse itself. Three kinds of changes occur, then, in our brains when the nerve impulses are passing—an electrical change, a chemical change, and a psychical change Which is the fundamental change?"
—The Psychological Clinic, Volume 11 [1918]
