attended with great difficulty ; there were no physiological labora- 

 tories, no instruments, no capable mechanicians to whom the physiolo- 

 gist could apply for assistance. Under these conditions, ingenuity and 

 resource were indispensable to success, and in these qualities Ludwig, 

 besides being conversant with the physical science of the time, was 

 pre-eminent. Accordingly, we find that two of the most important 

 of his early investigations were as much due to his ingenuity as an in- 

 ventor, as to his clear grasp of the physiological questions which his- 

 inventions were intended to elucidate. The most interesting of these- 

 inventions in its bearing on Ludwig's scientific career was that of 

 the kymograph (or, as he called it, the kymographion) •, for the know- 

 ledge gained by it was of so fundamental a character, that it in 

 great measure took the place of all that was before known as to the 

 relations of pressure to flow in the circulation. This instrument, of 

 which the use is to record the oscillations of a mercurial manometer 

 on a surface moving horizontally at a uniform rate, was first described 

 in a paper published in Midler's ' Archiv,' in 1847,* " On the Influence- 

 of the Respiratory Movements on the Blood-stream in the Aortic 

 System." Poiseuille had some ten years before used a similar mano- 

 meter to measure the lateral pressure exerted against the internal? 

 surface of the arterial system by the blood contained in it. This 

 pressure Ludwig desired to register automatically, and by so doing to 

 obtain a permanent record of the effects which are produced on the- 

 action of the heart and on the circulation by muscular movements. Ho 

 subsequently proceeded to examine in the same way those variations 

 in pressure and flow which depend on the incessantly varying func- 

 tional activity of organs, or on the direct action of the nervous 

 system. The general result of these early researches was to pave 

 the way for those later experimental investigations by which we have- 

 learned that the blood-stream is so controlled by the nervous system, 

 that the afflux of blood to each part is at every moment adapted to its 

 requirement. The discovery of the kymograph led to much wider 

 applications of the method of automatic inscription. Ludwig himself 

 applied it, as we have seen, to the recording of the movements of 

 respiration, as well as of the variations in arterial pressure. Subse- 

 quently, as elaborated by Chauveau and Marey, it became known as 

 the " graphic method," and it serves not only for the investigation of 

 animal movements of every conceivable kind, but even of the- 

 transient and delicate electrical changes which are associated with 

 vital action. 



Space does not allow me to do more than mention other con- 

 trivances of Ludwig for the study of the circulation, such, for 



* The original tracing of the first experiment with the kymograph is in the 

 Physiological Laboratory at Turin, having been given by Ludwig to Professor 

 Mosso, one of his most distinguished pupils. 



