4 86 THE SALIVARY GLANDS. 



as it is formed, is for the most part, at any rate, stored up in the cells in 

 the form of granules. 1 



Secondly, there is a taking up of proteid material by the cells. 2 This 

 occurs more or less exclusively in the outer part of the cells, and is the 

 chief cause of the formation of an outer non-granular zone. 1 The taking 

 up of fresh proteid substance is usually spoken of as a growth of proto- 

 plasm ; we may use the expression as a matter of convenience, bearing 

 in mind that a large portion of the fresh proteid substance may be 

 simply deposited in interstices or larger spaces of the protoplasm. 



It is probable also that, during the whole period of secretion, there is 

 a conversion of the newly taken up proteid into the material for 

 secretion, or, in other words, the protoplasm is continuously disappearing 

 and giving rise to granules. 



The loss of granules, together \vith the growth of protoplasm, causes 

 the gland to become less white and less opaque to the eye. 



The nucleus, as was first shown by Heidenhain, is more obvious, and the 

 nucleolus more conspicuous, in sections of the active gland than in those of the 

 resting gland. The shrunken state of the nucleus in the resting gland appears 

 to be due to the action of the hardening agent, for in teased glands, when the 

 nucleus is visible, without serious alteration in the normal form of the cell, it 

 is seen to be spherical. Nevertheless it is probable that there is some increase 

 in the organic substance of the nucleus during prolonged secretion. 



During rest 3 the protoplasm decreases and the granules increase, and 

 it would not be unnatural to suppose that no other changes take place in 

 the cells but those associated with the conversion of protoplasm into a 

 substance ripe for excretion. The point is one of great importance for 

 the proper understanding of the secretory processes. Is there or is 

 there riot during rest any interchange between the cells and the lymph, 

 beyond that of the taking up of oxygen and the giving off of carbonic 

 acid ? There is no experimental evidence to show whether the amount of 

 oxygen taken up by the gland cells is so much in excess of the carbonic 

 acid given off, that an increase in the weight of the gland takes place ; 

 but this is on general grounds probable enough, to prevent us from 

 attributing offhand any increase in weight which may occur in a gland 

 during rest to its cells having taken from the lymph proteid or substance 

 other than oxygen. 



We may take first the evidence that glands increase in weight 

 during rest. Obviously this is proved, if it can be proved that there is 

 a decrease in weight during secretion. 



Heidenhain stimulated the chorda tympani on one side in a dog, and, 

 after obtaining a considerable amount of saliva, killed the animal by 

 bleeding it, separated the glands on the two sides from their capsules, 

 and as far as possible from connective tissue, and then weighed them. 

 He found that the active gland weighed less than the resting gland. 



1 Langley, Journ. PhysioL, Cambridge and London, vol. ii. p. 261 ; Internal. Monatsclir. 

 f. Anat. u. HistoL, 1884, vol. i. p. 69 ; Proc. Roy. Soc. London, 1886, vol. xi. p. 362. 



2 Heidenhain, Arch. f. d, gas. PhysioL, Bonn, 1878, Bd. xvii. S. 43 ; Hermann's 

 "Handbuch," 1883 ; Lavdowsky, Arch. f. mikr. Anat., Bonn, 1877, Bd. xiii. S. 335. 



3 It is perhaps hardly worth while to defend the use of the word "resting" for a gland 

 which for some time has secreted but little, and the use of the word "active " for a #land 

 which for some time has been secreting more or less copiously. The words lead to no 

 ambiguity, and the objections to them appear to me purely pedantic. "Active" and 

 "resting," applied to any living tissue, are essentially relative terms ; it can hardly be 

 doubted that there is greater chemical change when secretion is going on than when it is not. 



