68 



PHYSIOLOGY 



CHAP. 



of puppy. (Lavdowsky.) 



n. 



sublingual. They are glands of the racemose type, i.e. they 



consist of acini, which are more or less saccular or tubular in 



shape, their cavities or alveoli communicating with one another 



by one or more branching excretory 

 ducts. The acini are surrounded by 

 a basement membrane consisting of 

 a network of flattened, nucleated, 

 branching cells, the meshes of which 

 are occupied by a delicate homo- 

 geneous substance. Inside the base- 

 ment membrane (Fig. 18) the secreting 

 cells form an epithelial lining which 

 bounds the alveolar cavity. The acini 

 are united into lobules, either by 

 blood-vessels or by loose connective 



tissue, which contains many lymph spaces and a rich network 



of blood capillaries. 



Two kinds of secreting cells can be distinguished in the alveoli, 



the serous or albuminous, and the mucous (Heidenhain). The 



serous cells, which secrete 



a thin fluid containing 



serum - albumin, exhibit 



in the resting state a 



protoplasm so richly infil- 

 trated with granules that 



the nucleus is obscured 



and becomes invisible. 



The mucous cells, which 



secrete a fluid that is ropy 



from the large amount of 



mucin, are large, clear, 



and spheroid when the 



gland is resting. They 



almost fill the alveolar 



cavity, their nuclei being 



invisible because they lie 



close to the basement 



membrane, and are 



pressed against it (Fig. Fi 



19). When all the alveoli 



of a gland are lined with 



albuminous cells (e.g. the 



parotid in man and almost all mammals, the submaxillary of rabbits, 



and certain glands that are scattered in the buccal mucosa), the 



gland, as a whole, is termed albuminous; when the alveoli are 



lined with mucous cells alone (e.g. part of the submaxillary in man, 



and the sublingual in all animals, and many simple buccal glands) 



.. 10. Section of part of human submaxillary gland. 

 (Heidenhain.) On the right, a group of mucous alveoli 

 with demilunes of Giannuzzi ; on the left, a group of 

 serous alveoli. 



