2G8 HISTOLOGICAL CHANGES. [BOOK IT. 



condition to the other successively observed. And sections of the 

 prepared and hardened gland of this or of any other animal tell nearly 

 the same tale. Thus in the pancreas of a dog which has been 

 fasting for about 30 hours, each secreting cell is found to consist 

 of two zones : an inner zone, studded with fine granules, and a 

 smaller outer zone, which is homogeneous or marked with delicate 

 striae, the nucleus being placed partly in the one and partly in 

 the other zone. When however the pancreas of an animal in full 

 digestion (about six hours after food) is examined, though the 

 whole cell is smaller, the outer homogeneous zone is found to be 

 relatively much wider, the granular inner zone being narrower, 

 and in some cases actually disappearing. If the pancreas be ex- 

 amined at the end of digestion, when its activity has once more 

 ceased, and it has entered into a state of rest, the outer zone is 

 again found to be narrow, the granular inner zone occupying 

 the greater part of the cell, which has once more become larger. 

 Carmine stains the outer zone easily, the inner zone with difficulty. 

 Hence when, as during activity, the outer zone is relatively large, 

 the cell as a whole seems more deeply stained than when, as during 

 rest, the outer zone is small. During activity the nucleus is large 

 and round; during rest it often appears irregular, owing to its 

 being in such a condition that it shrinks under the influence of the 

 reagents employed. 



Leaving aside for the present the changes in the nucleus, and 

 the matter of staining, we may say that the results of the two 

 methods are identical. 



Before, however, we attempt to explain what these results mean, 

 it will be well to pay attention for a while to another type of 

 secreting gland, the so-called mucous glands. We have already 

 seen that some salivary glands, such as the submaxillary of the 

 dog, secrete a thick viscid saliva, the viscidity being due to the 

 presence of the body mucin (see Appendix), the essential con- 

 stituent of the so-called mucus ; while other salivary glands, such 

 as the parotid of most animals, secrete a thin limpid saliva free from 

 mucin. Glands of the latter kind, from the nature of their secre- 

 tion, receive the name of 'serous' glands. Glands, however, which 

 give rise to a viscid mucin-holding secretion, always contain a 

 certain number of cells of a distinct type. These cells are called 

 'mucous cells;' and the glands in which they are found are called 

 'mucous glands.' Sometimes the mucous cells are abundant form- 

 ing a large part of many or most of the alveoli; sometimes they are 

 scanty. Each ' mucous ' cell when examined in a fresh and natural 

 condition is loaded throughout with somewhat large granules; 

 but when treated with alcohol or other hardening reagents 

 (Fig. 51 A) appears to consist of two parts: of a small quantity of 

 what we may speak of as ordinary protoplasm, readily staining 

 with carmine, &c. and gathered round the nucleus, which is 

 placed towards the outside of the cell, generally close to the base- 



