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 (05 per cent. HC1) or an alkaline salt (5 per cent. ]S T a a C0 3 ) 
is injected into the gland duct. 1 In this case, oedema is slowly pro- 
duced; rapidly, however, if the chorda tympani he 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 now 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, Bcr. <1. J:. s<irhs. Gescllsch. d. Wissensch., 1865. 
- Ztschr.f. rat. Med., 1851, N. F., Bd. i. S. 271. 
3 Stud. d. physiol. Inst, zu Brcslau, Leipzig, S. 69. 
