378 



Mr. J. N. Langley on the Structure of [Xov. 27, 



causing a secretion in the glands, produces the most striking effects on 

 the blood circulation ; the current all but ceases. 



The resting gland thus viewed shows alveoli, in which the 

 boundaries of the cells are faintly marked out by light lines between 

 the many granules that fill the cells. The granules stretch from 

 lumen to basement membrane. TsTo nuclei are to be seen in the 

 alveoli, nothing but a mass of not very refractive granules with an 

 indistinct network of light lines which mark the separate cells. 



The secreting gland similarly viewed strikes the eye at once as being 

 much more transparent ; with a low magnifying power, the lobules 

 even when thick, are no longer the dense dark masses of the resting 

 gland. With a Zeiss D or E objective, it is seen that this is caused by 

 the disappearance of the granules at the outer part of the alveoli, the 

 part near the basement membrane. The later the stage of secretory 

 activity, the larger the non-granular clear zone. It is however only in 

 the earlier secretory stages that the clear portion is in the form of 

 a ring in section, later the clear zone dips down at fairly regular 

 intervals towards the lumen. The granules thus acquire a star- 

 like arrangement. This comes about in the following manner: — As 

 secretion goes on, the cells draw away from one another slightly at the 

 lumen, and at their sides contiguous to the lumen (perhaps because 

 they are there being used up) : so that the lumen can be more or less 

 distinctly seen with short prolongations running out between the 

 cells ; at the same time the granules disappear more rapidly from the 

 interior than from the periphery of the cells, hence the granules become 

 arranged in a clump at the luminar margin, and stretch out from this 

 some little distance along the cell sides. 



The rather troublesome method given above is not necessary for 

 the observation of the living condition of the tissue ; small pieces cut 

 out and mounted without the addition of fluid preserve for a short 

 time very closely their normal appearance. If to such a specimen 

 any of the ordinary indifferent fluids be added, the granules become 

 more highly refractive, and later a thorough alteration takes place in 

 the cells, the granules originally present to a large extent at any rate 

 disappear and others are formed. 



A very satisfactory and economical method of noting the changes 

 which take place in the gland during secretion, is to narcotise an 

 animal and then to snip out small bits from various parts of the gland 

 at different stages of sympathetic stimulation or pilocarpin injection. 

 The alveoli, at first granular throughout, become less and less so, until 

 hardly any granules are to be seen. At this later stage very little 

 saliva can be obtained. 



The cells, during the process of losing their granules, become 

 -much smaller ; the reparation is not sufficient to cover the waste. 



I may remark that it does not necessarily happen that every hungry 



