566 REPORT— 1882. 



the great man, wlio at Marburg, at Vienna, and at Leipzig, bas won for himself 

 the right to be called at once the greatest physiologist, and the greatest teacher of 

 physiology, of his time. 



1. Ludwif/s Discovery of Secreting Nerves. 



It was in the year 1851 that Lndwig first announced to the scientific world ' 

 the fact that the secretion of the salivary glands is under the influence of the 

 nervous system. C. G. Mitscherlich, as Ludwig points out, had surmised that the 

 secretion of saliva only occurs as the residt of a stimulation of certain nerves, i.e. 

 the nerves of taste and the nerves supplying the muscles of mastication. No 

 attempt had, however, been made, before Ludwig's, to ascertain experimentally 

 whether the stimulation of nerves supplying glands influenced directly their secre- 

 tion. As a subject of study Ludwig chose the submaxillary gland. He found 

 that on stimulating by a succession of induction shocks the nerve-twigs proceeding 

 from the lingual branch of the fifth nerve, and which accompany Wharton's duct 

 to the gland, secretion of saliva occurred, so long as the excitability of the nerves 

 persisted. 



In experiments performed in conjunction with his pupil Rahn, Ludwig found 

 that secretion occurs on direct .stimulation of the glandular nerves, even when the 

 circulation has been arrested for a time, as, for instance, when the contractions of 

 tlie heart are inhibited for some time. 



2. Ludwig's Discovery that Secretion is not a Process directly d^iendent upon the 



Arterial Pressure. 



In the paper which I have alread}' quoted, Ludwig published the results of the 

 following experiments. A mercurial gauge was placed in communication with the 

 duct of the submaxillary gland, the height of the mercury in the gauge being re- 

 corded (by means of a float to which was attached a writing point) upon the 

 travelling surface of the kymographion, the instrument which Ludwig had con- 

 trived for permanently recording the amount and variations of the blood-pressure in 

 arteries and veins. At the same time, another gauge placed in communication with 

 the carotid artery, or one of its branches in close proximity to the gland, recorded 

 the height of the blood-pressure on the same travelling surface. On stimulating- 

 the secretory nerves, Ludwig found that saliva was poured out long after the 

 pressure exerted by it upon the interior of the gland (as measured by the height to 

 which the mercury was raised in the gland-duct manometer) exceeded the pressure 

 of blood in the arteries. Thus in his first recorded experiment the mean pressure 

 of blood in the carotid artery amounted to IOS'5 millimetres of mercury, whilst 

 during a stimulation of the nerve-filaments going to the gland, the pressure in the 

 gland-duct manometer rose to between 11)0'7 and 196'5 millimetres, i.e. indicated 

 that the pressure exerted by the fluid, secreted under the influence of nerve-stimu- 

 lation, exceeded the arterial pressure by an amount corresponding to a column of 

 mercury about 3^ inches high. It is obvious that the experiment at once and con- 

 clusiveW proved that the secretion of a watery liquid like the saliva may be brought 

 about by a process altogether diflferent from a process of filtration ; for in filtration 

 the passage of liquid through the minute pores of the filter necessarily depends 

 iipon a difference in pressure on the two sides of the filter, the movement of liquid 

 being from the side of greater to that of less pressure. 



In this brief sketch I have only time to refer to the most salient of the early 

 discoveries of Ludwig on secretion, and must pass over without comment tlie first 

 experiments by which he showed the influence exerted by variations in the strength 

 of the stimulus of a secretory nerve upon the amoimt and chemical composition of 

 the secreted liquid. 



' Ludwig, ' Neue Versuche iiber die Beihilfe der Nerven zur Speichelabsonderung,' 

 Henle v<i Pfeifer's Zeitschrift, New Ser., vol. i. (1851), p. 255. 



