CARL LUDWIG. 165 



which influence the calibre more especially of the small 

 arteries. Could the physiology of salivary secretion be 

 explained by this new mechanism ? Ludwig by ingenious 

 experiments soon showed that in salivary secretion there 

 was another influence at work beside the action of vaso- 

 motor nerves, viz., the action of glandular or secretory 

 nerves, so that one of his great discoveries was the exist- 

 ence of a separate class of nerves now known as " secretory 

 nerves ". 



But perhaps Ludwig's greatest interest was the doctrine 

 of the source and movements of the various juices of the 

 body, more especially of the blood and lymph, and here we 

 have to deal with an amazing number of contributions. 

 Indeed, in no other laboratory have the phenomena con- 

 nected with the movements of these fluids been so 

 thoroughly investigated as in that of Ludwig. The 

 arrangement of the muscular fibres of the heart early 

 attracted his attention, but to him this meant more than 

 merely to describe their arrangement. He sought to 

 explain this arrangement, and how it was useful to the 

 heart to enable it to empty itself, why also the right 

 ventricle forms a crescent-like cavity round the left ven- 

 tricle, while by a study of the arrangement of the fibres 

 around the auriculo-ventricular orifices he showed how 

 important it was from the point of view of preventing the 

 reflux of blood into the auricles during systole that these 

 orifices contracted, thus affording at the same time a better 

 point d'appui for the segments of the auriculo-ventricular 

 valves, the arterial orifices at the same time remaining 

 unchanged in their dimensions. 



Ludwig's name, however, will remain indissolubly con- 

 nected with his epoch-making invention of his " Kymo- 

 graph " or " Kymographion " or "Wave-writer," an instru- 

 ment to be found in all laboratories. The importance of 

 this invention is twofold : first, on account of its practical 

 value as a means of measuring the pressure exerted by the 

 blood upon the inner surface of the larger blood-vessels, 

 i.e., the blood pressure, but second, because by it Lud- 

 wig founded the graphic method in physiology, a method 



