Chap, xviii.] SECRETIONS AND EXCEETIOITS IN PAETICULAE. 267 



Tte function of the salivary glands is much more simple than 

 that of the liver. The culs-de-sac or acini of the salivary glands 

 in cluster are lined with epithelial cells whichh^ive a single nucleus. 

 These cells, flattened and pavimentous, in the state of repose 

 of the gland, swell and soften during the period of secretion. 

 It is then that they take from the blood the materials necessary 

 for the fabrication of ptyaline ; also they become loaded with 

 granulations, which give them a slighly opaque look. 



Though identical in appearance, the diverse salivary glands 

 of man and of the superior mammifers secrete, that is to say 

 fabricate, coagulable substances specially appertaining to each 

 gland. There are here imperceptible particularities, belonging 

 to the molecular acts themselves of nutrition. The fact becomes 

 more striking still if we range the poison glands of reptiles 

 with the salivary glands; a classification justified moreover by 

 anatomy. 



The salivary cells swell assuredly during the period of 

 glandular activity, but it is especially during repose that they 

 seem to detach themselves from the partition and to accumulate 

 in the culs-de-sac. Then, when the ^land commences to operate, 

 a liquid flow, borrowed from the blood, traverses the wall of 

 the acini, and goes to dissolve and to carry along the salivary 

 ferment previously formed. Analogous phenomena are produced 

 in the lactiferous glands, and perhaps in most of the glands. 

 In the lacteal glands the secretory cells load themselves with 

 droplets of fat, which their rupture sets at liberty. 



The fundamental structure of the excretory glands does not 

 perceptibly differ from that of the secretory glands. The 

 mechanism of their functions is also the same. In excretion as 

 in secretion there are always cells, called epitMial, which borrow 

 from the blood of the fia^illaries certain substances ; but the 

 secretory cells content themselves with giving a passage to the 

 substances substracted without perceptibly modifying them. 

 The most important of all the excretions is certainly the urinarj- 

 or renal excretion. 



