fully applied to resist poisoning by carbonic oxide. This gas, formed by the combustion of charcoal and the oxygen of air, is a powerful poison. Breathed in moderate quantity, it induces death by well-defined action; the carbonic oxide, acting on the blood-globules, displaces their oxygen, and forms a stable combination with them, which is inert as regards vital properties. The constituent elements of the organs soon cease to act, and they die as they do after arterial hæmorrhage. For some hours, immediately after the poisoning, the blood-globules only are concerned, the other tissues remaining untouched; it will be enough, then, to restore a healthy state, to empty the vascular system, and replace the poisoned blood by new blood, and life will revive. Thus the history of transfusion once more proves that triumphs in the healing art may find their starting-point in the physiologist's table, as advances in industrial art often originate in the chemist's alembic.
In the centuries regarded as a whole, the epoch of Harvey and our own seem to belong to a similar period. The demonstration by physiology of the individual life of the parts, and the practical applications of transfusion, are wholly modern, as the circulation of the blood itself is. In ancient days the general belief was, that the life dwells in the blood, and yet some ancients seem to have had a suspicion that the elements of the organization live of themselves, and that, perhaps, the blood has a movement of circulation. Yet the ancients observed the life of the parts only in their outward forms. It is as a child studies the works of a watch: give it to him, and he is satisfied to hear it tick; open it, and he follows with his eye the movement of the wheels, but does not go further than to note appearances. Progress comes with age, and the child, seeing the same watch when he is a grown man, asks why and how it goes; taught by experience, by dint of perseverance and labor, he takes off and replaces every wheel, gains a precise idea of the mechanism of each part, and the arrangement of the whole is then clearly understood. Men of science in our times have studied the human machine so: the life of the parts has not only been observed, but traced and detected in its most secret machinery. Transfusion of blood, so useful in this respect, never acquired any true scientific importance in the seventeenth century. At first it appears as a universal panacea, aiming at the mastery of life, and triumph over disease itself. We have seen how the mere imaginings of that idle dream passed away. In our day the true method, the method of observation, is rightly honored, and scientific questions, no longer agitated with mere parade of eloquence, are modestly studied by their facts in the seclusion of laboratories. Transfusion again comes up, but not with its old extravagant pretensions; it no longer aspires to give universal, indefinite life. Reduced to the simple duty of a scientific process, it unveils the most mysterious secrets of the organization; it throws light upon the life
