in the debatable land between physiology and psychology, and have contributed to the advance of both sciences.
The history of these discoveries illustrates in a very striking manner the unexpected developments to which scientific research sometimes leads. In 1873-'74 Dr. Mosso experimented in the laboratory of Professor Ludwig, at Leipsic, upon the circulation of the blood through the kidney. He took advantage of the fact that death is a double process: 1. The death of the animal as a whole, or that which we ordinarily call death; and, 2. The subsequent and gradual death of the tissues, to which is due the curious phenomenon that an organ survives the animal of which it has formed a part. The most remarkable and familiar instance of this is the heart of the frog or turtle, which may continue to beat, for several days even, after the animal to which it belonged has been killed. So also the vitality of the kidney may be preserved by proper precautions for a considerable period. The organ overlives, as it is expressed in German. To physiologists this overliving of tissues is of the utmost value, because it enables them to perform numerous experiments that would otherwise be difficult or impossible, which latter alternative would have been the case with Mosso's researches upon the renal circulation.
Mosso's experiments were briefly as follows: Their connection with the subject of this article will appear directly. The kidney was taken from a dog immediately after his death, and glass tubes inserted into the artery and the vein, so that blood could be passed through the former into the kidney, under any desired pressure, sufficient to force it through the vessels of the organ into the vein, whence it could pass out by the glass tube, and be collected in a receptacle. It is unnecessary to describe the details of the experiments—the ingenious devices adopted to prevent the drying up of the kidneys, or irregularities of the pressure of the blood; in short, to eliminate those conditions which might disturb the accuracy of the results. Let it suffice to say that the kidney after its removal from the body was found to preserve its vitality to a fuller extent than had been previously supposed. The especial result of Mosso's experiments was the demonstration of the alterations of the circulation which take place in a single organ independently of the central nervous system, from which the kidney was of course entirely severed. It was noted among other things that the capacity of the blood-vessels altered: under one set of circumstances the kidney held more, under another less blood. This could be detected in two ways: first, when the capacity increased, more blood would enter the artery than flowed out from the vein, or, if the capacity diminished, more would flow out than in; and, second, by changes in the volume of the kidney. The latter method was the most valuable, because the changes in the volume could be actually measured. This was accomplished by placing the kidney in a glass case filled with oil. The tubes for the artery and the vein passed out through the side of the case.
