TBANSACTIONS OF SECTION D. — DEPT. ANATOMY AND PHYSIOLOGY. 567 



3. Ludxcig's Discovery that during Secretion Heat is evolved in Glands. 



Pursuing his researches on the salivary glands, Ludwig some years later,' in 

 conjunction with his pupil Spiess, discovered 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 tem- 

 perature nearly three degrees Fahr. (1'5° 0.) 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 process of secre- 

 tion was even greater. From the fact that the saliva is a liquid containing but 

 three or four or hve parts of solid matters to one thousand of water, it would scarcely 

 have been surmised, upon a merely physical hypothesis, that its production 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 Reseakches op Schipf, Ecehaedt, and Claude Bernaed, ox 



THE SeCEETOKY NeRYES OF THE SALITAEY 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 correctness of Schiff's supposition that the abundant secretion which 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 also, the 

 gland is under the direct control of two orders of nerve-fibres. The first are con- 

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

 derived from the facial nerve, and, when stimulated, lead to au 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 fiow 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 tiuid 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 passing through it was 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 fiow of blood through the gland and into 

 the veins, the blood presenting under these circumstances au intensely venous hue. 



The facts just referred to ajjpeared reconcilable at first with tbe 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 



' Ludwig u. Spiess, Sitzungshcr. d. Wiener Altad. Mathem. u. Naturwissenschaft : 

 Class, vol. xxT. (1857), p. 548. 



