THE SECRETOR Y PRESSURE. 5 1 1 



when the gland secretes, an additional amount is formed exactly equal 

 to that of the fluid in the saliva secreted, a conclusion which it is not 

 easy to accept. 



In two conditions oedema of the gland is obtained : First, when 

 dilute acid (O5 per cent. HC1) or an alkaline salt (5 per cent. Na 2 CO 3 ) 

 is injected into the gland duct. 1 In this case, oedema is slowly pro- 

 duced; rapidly, however, if the chorda tympani be stimulated, though 

 no secretion follows. There can be little hesitation in attributing this 

 to the injury inflicted on the walls of the small vessels ; for damage of 

 the vessels, as we know, largely increases the amount of the lymph 

 formed in any given condition. Secondly, when there is a considerable 

 resistance to the flow of saliva from the duct. On continued stimulation 

 of the chorda in such cases, the lobules become separated by a mucous 

 fluid, and there is great oedema. At first this fluid consists simply of 

 filtered saliva ; later, probably, lymph is added, partly in consequence of 

 a direct injury to the vessels, and partly, as suggested by Heidenhain, in 

 consequence of pressure on the vein. 



THE SECRETORY PRESSURE. 



Ludwig 2 was the first to show, by experiment on the submaxillary 

 gland of the dog, that the secretory pressure may overpass considerably 

 the blood pressure. Thus in one case he obtained a pressure of 190 mm. 

 of mercury from the saliva caused to flow by stimulating the chordo- 

 lingual nerve, although the blood pressure in the carotid artery was only 

 112 mm. of mercury. Since that time considerably higher pressures 

 have been obtained from chorda saliva ; the maximum pressure observ- 

 able in any one species is, broadly speaking, the greater, the larger the 

 individual. 



On connecting Wharton's duct with a mercurial manometer, and 

 stimulating the chorda tympani, the pressure rises at first rapidly, then 

 more and more slowly ; when the maximum pressure is attained, a 

 cessation of the stimulus is followed by a fall of pressure, due to filtra- 

 tion taking place between the cells of the ducts and of the alveoli. 

 When the observation is at all frequently repeated, the lobules of the 

 gland become separated by mucous fluid, the pressure attained becomes 

 less, and the irritability of the gland greatly decreases. 



In the parotid gland of the dog, the observed secretory pressure is 

 less than in the submaxillary gland, usually being 100 to 130 mm. of 

 mercury, but the difference is probably due to the limpidity of the 

 parotid saliva, which allows a more rapid filtration. 



The pressure of the sympathetic secretion may also exceed that 

 of arterial blood. In experimenting with a mercurial manometer, the 

 pressure should be raised artificially to about 150 mm. of mercury 

 during the first stimulation of the sympathetic, the connection of the 

 manometer with Wharton's duct clamped for about thirty seconds, 

 and then undamped and the sympathetic again stimulated. Heiden- 

 hain, 3 in an experiment on the submaxillary gland of a dog, found 

 that the sympathetic saliva was secreted at a pressure of 150 to 160 

 mm., whilst the pressure of the chorda saliva was 250 to 270 mm. 



1 Giamizzi, Ber. d. k. sacks. Gesellsch. d. Wissensch., 1865. 



2 Ztschr.f. rat. Med., 1851, N. F., Bd. i. S. 271. 



3 Stud. d. physiol. Inst. zu Breslau, Leipzig, S. 69. 



