CHAP, xviii.] SECRETIONS AND EXCRETIONS IN PARTICULAR, 267 



The 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 whichhave a single nucleus, 

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

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

 Jt 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 

 Imore 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 

 iglandular 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 gland commences to operate, 

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

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

 Iferment previously formed. Analogous phenomena are produced 

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

 jln the lacteal glands the secretory cells load themselves with 

 j 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 

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

 Jin secretion there are always cells, called epithelial, which borrow 

 : from the blood of the capillaries certain substances ; but the 

 1 secretory cells content themselves with giving a passage to the 

 : substances substracted without perceptibly modifying them. 

 1 The most important of all the excretions is certainly the urinary 

 ' or renal excretion. 



