226 AN AMERICAN TEXT- BOOK OF PHYSIOLOGY. 



Recent work by Ranvier, Drasch, Biedermann, and others has called atten- 

 tion to an interesting phenomenon occurring in gland-cells during secretion 

 which when better known will possibly throw light upon the formation of the 

 water stream under the influence of nerve-stimulation. Ranvier 1 describes 

 in both serous and mucous cells the formation of vacuoles within the proto- 

 plasmic substance. These vacuoles are particularly abundant after nerve- 

 stimulation. They seem to contain water, and if they behave as they do in 

 the protozoa — and this is indicated by the observations of Drasch 2 upon the 

 glands in the nictitating membrane in the frog — they would seem to form a 

 mechanism sufficient to force water from the cells into the lumen. 



Histological Changes during Activity. — The cells of both the albu- 

 minous and mucous glands undergo distinct histological changes in conse- 

 quence of prolonged activity, and these changes may be recognized both in 

 preparations from the fresh gland and in preserved specimens. In the parotid 

 gland Heidenhain studied the changes in stained sections after hardening in 

 alcohol. In the resting gland (Fig. 53) the cells are compactly filled with 



Fig. 53.— Parotid of the rabbit, in the resting condition (after Heidenhain). 



granules that stain readily and are imbedded in a clear ground substance 

 thai does not stain. The nucleus is small and more or less irregular in out- 

 line. After stimulation of the tympanic nerve the cells show but little altera- 

 tion, but stimulation of the sympathetic produces a marked change (Fig. 54). 

 The cells become Bmaller, the nuclei more rounded, and the granules more 

 closely packed. This last appearance seems, however, to be due to the hard- 

 ening reagents used. A truer picture of what occurs may be obtained from a 

 Mu.lv of sections of the fresh -land. Langley, 3 who first used this method, 



1 Comptes rendus, cxviii., 1, p. K'> s . 2 Archivfiir AnatomU wnd 1'lojsiologie, 1889, S. 96. 

 8 Journal of Physiology, 1879, vol. ii. p. 260. 



