SECRET1OK 399 



constituents oi the secretion according to the composition of the 

 lymphatic and blood-plasma. To this style of secretion belong the 

 water of the urine, the sweat, and the tears. The most important 

 principles filtered are water, salts of the plasma, chlorides of potas- 

 sium, sodium phosphates, lime, magnesia, and carbonic acid. 



2. Secretion Proper Production of New Principles. Here 

 glandular activity especially intervenes; the epithelial cell does not 

 act as a simple filter. It modifies the nature of those products pass- 

 ing through it, or creates from them new products. In this class 

 may be put the digestive secretion. The products thus formed by 

 gland-cells vary for each gland; neither physiology nor histology is 

 able to explain their manner of production. Thus, we are not able 

 to explain in a satisfactory manner the chemical changes which make 

 hydrochloric acid appear in the gastric juice, sulphocyanide of potas- 

 sium in the saliva, bile acids in the bile, etc. 



3. Secretion by Glandular Desquamation. In the preceding 

 types of secretion the gland-cell preserves its integrity; it does not 

 do anything else except to allow the external materials to pass 

 through it, changed or unchanged. However, in this type the cell 

 itself falls and is eliminated to contribute to the formation of the 

 product of secretion. This glandular desquamation is comparable to 

 the epithelial desquamation which occurs during the life-history of 

 the epidermis. Generally this desquamation is preceded by a chem- 

 ical change of the gland-cells. This change is fatty, as in sebaceous 

 secretion. The sebaceous fats and mucin form the special products 

 of this group of secretions. 



4. Morphological Secretion. In this type the essential element 

 of the secretion is a formed element. It is a specialized cell derived 

 from a cell, together with a liquid which holds this anatomical ele- 

 ment in suspension. Such is the spermatic fluid. 



Secretion Defined. The term secretion has been defined as the 

 result of the special activity of the glandular tissues. It is the elab- 

 oration of fluid or semifluid mixtures by selection and formation 

 from the fluids which surround the active cells, as well as from the 

 substances of the cells themselves. Up to a certain point secretion 

 is composed of two acts which are separated by a distinct line of 

 demarcation. 



1. Lymph passes through the wall of the capillary. This 

 lymph spreads into the lymph-spaces which surround the acini, and 

 it is from this lymph that the elements are taken out for the pro- 

 duction of the secretory products. The filtration is tinder the 





