304 THE POPULAR SCIENCE MONTHLY. 



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 man- 

 ner the unexpected developments to which scientific research sometimes 

 leads. In 1873-74 Dr. Mosso experimented in the laboratory of Pro- 

 fessor 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 remark- 

 able 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 dif- 

 ficult 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 unneces- 

 sary 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 vital- 

 ity 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 kid- 

 ney 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 accom- 

 plished 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. 



