August 24, 1882] 



NA TURE 



411 



tion shocks the nerve twigs proceeding from the lingual branch 

 of the fifth nerve, and which accompany Wharton's duct to the 

 gland, secretion of ssliva 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 the heart 

 are exhibited for some time. 



2. Ludwig's Discovery that Secretion is not a Process directly 

 dependent upon the Arterial Pressure. — In the paper which I 

 have already quoted, Ludwig published the results of the 

 following experiments. A mercurial gauge was placed in com- 

 munication with the duct of the subm ixillary glind, the height 

 ot the mercury in the guage being recorded (by means of a 

 float to which was attached a writing point) upon the travelling 

 surface of the kyimgraphion, the instrument which Ludwig had 

 contrived for permanently recording the amount and variations 

 of the blood pressure in arteries and veins. A* 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 108 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 1907 and 

 196'S millimetre-, i.e., indicated that the pressure exerted by 

 the fluid, secreted under the influence of nerve stimulation, 

 exceeded the arterial pressure by an amount corresponding to 

 a column of mercury about 34 inches high. It is obvious that 

 the experiment at once and conclusively proved that the secre- 

 tion of a water)- liquid like the saliva may be brought about by 

 a process altogether different from a process of filtration ; for in 

 filtration the passage of liquid through the minute pores of the 

 filter necessarily depends upon a difference in pressure on the 

 two sides of the filter, the movement of liquid being from the 

 side of greater to that of lesser 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 the fir»t experiments by which 

 he showed the influence exerted by variations in the strength 

 of the stimulus of secretory nerve upon the amount and chemical 

 composition of the secreted liquid. 



3. Ludwig 1 s Biscoz'ery that during Secretion Heat is evolved 

 in Glands. — Pursuing his researches on the salivary glands, 

 Ludwig. some years later, (Ludwig u. Spiess, " Sitzungsber. d. 

 Wiener Akad. Mathem. u. Naturwissenchaft : Classe," vol. 

 xxv. (1857), p. 548,) in conjunction with his pupil Spiessi dis- 

 covered that, when a gland is thrown into action by stimulation 

 of its nerves, heat is evolved. In the case of the submaxillary 

 gland, for instance, he found that the saliva which was secreted 

 might have a temperature nearly three degrees Fahr. (l'5* C. ) 

 above that of the blood going to the gland. Important as was 

 this result because of the light which it threw upon the source 

 of animal heat, its value as bearing upon the nature of the pro- 

 cess of secretion was even greater. From the fact that the 

 saliva is a liquid containing but three or four or five parts of 

 solid matters to one thousand of water, it would scarcely have 

 been surmised, upon a merely physical hypothesis, that its pro- 

 duction would have been attended by any considerable evolution 

 of heat. The evolution of heat is indeed one of the strongest 

 proofs we have that the act of secretion is the result of the 

 living activity of those ultimate units of the glands, the gland 

 cells ; but to this I shall revert hereafter. 



The Researches of Schiff, Eckhardt, and Claude 

 Bernard, on the Secretory Nerves of the Salivary 



GLANDS. 



The study of the innervation of the salivary glands which had 

 been commenced by Ludwig and Rahn was continued with great 

 success by other observers, and particularly by Claude Bernard 

 and Eckhardt. The first of these observers proved the correct- 

 ness of Schiff's supposition that the abundant secretion w-hich 

 followed the stimulation of fibres of the fifth cranial nerve was in 

 reality due to the presence of fibres of the chorda tympani mixed 



with them. It was Eckhardt, however, and afterwards Claude 

 Bernard, who established the remarkable fact that, in the case 

 of the submaxillary gland, and, as has since been shown, of 

 some other glands als:>, the gland is under the direct control of 

 two orders of nerve fibres. The first are contained in branches 

 of cranial nerves, and in the case of the submaxillary gland are 

 derived from the facial nerve, and, when stimulated, lead to an 

 abundant secretion of watery saliva, relatively rich in saline and 

 poor in organic constituents ; the second are contained in the 

 so-called sympathetic nerve trunks distributed to the gland ; 

 and these, when stimulated, occasion an exceedingly scanty 

 flow of very concentrated and highly viscid saliva, containing a 

 relatively large quantity of organic constituents, particularly of 

 mucin. 



Claude Bernard now pointed out that stimulation of the 

 above-mentioned nerves leads to changes in the circulation of 

 blood through the gland, in addition to the changes in the 

 amount and quality of the fluid secreted by it. 



Thus stimulation of the cerebral fibres supplying the chorda 

 tympani was found to produce a great dilatation of the arteries 

 of the gland ; so that the amount of blood pas-ing through it w as 

 very largely increased, that passing out through the venous trunks 

 of the gland presenting a florid arterial colour instead of the 

 brown venous hue observed when the gland was not secreting. 

 Stimulation of the sympathetic fibres, on the other hand, caused 

 a great contraction of the glandular arteries, consequently a 

 diminution of the flow of blood through the gland and into the 

 veins, the blood presenting under these circumstances an intensely 

 venous hue. 



The facts just referred to appeared reconcilable at first with the 

 view that the secretion of saliva, as a result of nerve stimulation, 

 was primarily dependent upon changes in the circulation of blood 

 through the gland ; though, upon reflection, the surmise was 

 negatived by some of the facts discovered long before by Ludwig, 

 and particularly by that, already referred to, of glandular secretion 

 following stimulation of glandular nerves, even where the 

 circulation has been stopped, as by cardiac inhibition. 



Bernard's experiments had unquestionably established that 

 in addition to nerves which, when stimulated, occasioned 

 the contraction of arteries — "the vaso-motor" or, as we now 

 sometimes call them, the " vaso-constrictor " nerves — there are 

 others which when stimulated occasion, on the contrary, the 

 dilatation of arteries — the so-called " vaso-inbibitory " or "vaso- 

 dilator" nerves. That it was not stimulation of the vaso- 

 dilator nerves, which, by increasing the amount and the pressure 

 of the blood flowing through the capillaries, occasioned the 

 secretion of saliva, was shown by several experiments, but 

 especially by an observation of Keuchel. This observer found 

 that the alkaloid of the deadly nightshade, viz. atropia, when 

 introduced into the system, exerts such an action, that on stimu- 

 lating the chorda tympani no secretion of saliva follows ; whilst, 

 on the other hand, dilatation of the arteries is produced exactly 

 as under normal circumstances. Other drugs have since been 

 discovered which exert a similar action to that of atropia in 

 paralysing secretory nerves, whilst some are now known which 

 antagonise the action of atropia, and restore the suspended 

 activity of the secretory nerves. From these studies has un- 

 questionably resulted a knowledge of the conclusion, that 

 although the process of secretion is favourably influenced by the 

 vascular dilatation which follows the state of activity of the 

 vaso-dilator nerves, the actual process of secretion is not due to 

 them, but, so far as it is controlled by the nervous system, is 

 directly under the influence of certain nerves which may be 

 termed secretory. 



Discoveries which show that Secretion, though in- 

 fluknced by, is not necessarily dependent upon, 

 Stimulation of Nerves going to a Gland. 

 A knowledge of the facts which I have brought before you • 

 hitherto would "of itself lead you to suppose that glandular 

 secretion is a process which is in abeyance except under the in- 

 fluence of stimulation of nerves which throw the gland into 

 activity, in the same manner as the quiescent muscle passes into 

 activity normally, only when its motor nerves are stimulated. 

 But this supposition, though it may be in some measure true in 

 the case of certain glands, is not borne out by a study of se- 

 creting glands in general — a study which teaches us that whilst 

 the activity of the gland cells may be, and often is, remarkabl 

 under the control of the nervous system, it is by no means 

 necessarily dependent upon it. The activity of the gland de- 



