SECRETION PHYSIOLOGY. 309 



and alveoli are compressed and the liquid in them ejected. If 

 that liquid is thin and runs readily, as in most albuminous 

 glands, for example the parotid and submaxillary of the rabbit, 

 sheep and horse, and the cat's submaxillary, or in mucous 

 glands after long stimulation, the latent period is short, and 

 the saliva is all expelled in from 10—20 seconds. Thereafter, 

 although contraction persists, no more secretion escapes. If, 

 on the other hand, the saliva is viscid, as in the first stim- 

 ulation of a previously resting mucous gland (submaxillary and 

 parotid of dog), it offers a great resistance in passing through 

 the fine ducts and consequently requires a greater pressure and 

 a longer time to start and to expel. Consequently the latent 

 period is long and the secretion persists for some time. This 

 explains the anomalous cases represented by Experiment III. 

 In cases of very great viscidity, as in the parotid gland of the 

 dog, the resistance may even be too great to be overcome by the 

 compressing strength of the tissues. In this gland stimulation 

 of the symyathetic either causes no secretion at all or very lit- 

 tle, unless the saliva in the gland be previously diluted by the 

 action of the dilator nerve. The muscular theory, too, readily 

 explains why a typical sympathetic secretion can ensue in the 

 total absence of blood supply. 



b. The Decrease in the Amount of Saliva Obtainable upon 

 Several Successive Stimulations. 



If one sympathetic stimulation be followed by several others 

 the amount of saliva obtainable on the second, or following 

 stimulations, is much less than the first, and may be nothing at 

 all.* If, however, the gland be allowed to rest, or if the chorda 

 be stimulated, the nerve again produces a copious secretion upon 

 sympathetic stimulation. This is shown in the following ex- 

 cerpts from experiments on the dog's and cat's submaxillar}^ 

 Readings in mm. Stimulation in each case for thirty seconds. 

 It is also clearly seen in Experiment VII, p. 311. 



* This phenomenon has, of course, been often described. See among others 

 Langley.39 



Annals X. Y. Acad. Scl, XI, September 12, 1898 — 21. 



