4io SECRETIOK. 



placed on the surface or in the cavity whence the secretion 

 is poured. 2nd. That many secretions which are visible 

 with the microscope may be seen in the cells of their 

 glands before they are discharged. Thus, bile may be 

 often discerned by its yellow tinge in the gland-cells of the 

 liver ; spermatozoids in the cells of the tubules of the 

 testicles ; granules of uric acid in those of the kidneys of 

 fish ; fatty particles, like those of milk, in the cells of the 

 mammary gland. 



The process of secretion might, therefore, be said to be 

 accomplished in, and by the life of, these gland-cells. 

 They appear, like the cells or other elements of any other 

 organ, to develop themselves, grow, and attain their indi- 

 vidual perfection by appropriating the nutriment from the 

 adjacent blood-vessels and elaborating it into the materials 

 of their walls and the contents of their cavities. In this 

 perfected state, they subsist for some brief time, and when 

 that period is over they appear to dissolve or burst and 

 yield themselves and their contents as the peculiar material 

 of the secretion. And this appears to be the case in every 

 part of the gland that contains the appropriate gland-cells ; 

 therefore not in the extremities of the ducts or in the acini 

 alone, but in great part of their length. 



In these things there is the closest resemblance between 

 secretion and nutrition; for, if the purpose which the 

 secreting glands are to serve in the economy be disre- 

 garded, their formation might be considered as only the 

 process of nutrition of organs, whose size and other con- 

 ditions are maintained in, and by means of, the continual 

 succession of cells developing themselves and passing 

 away. In other words, glands are maintained by the 

 development of the cells, and their continuance in the 

 perfect state : and the secretions are discharged as the 

 constituent gland-cells degenerate and are set free. The 

 processes of nutrition and secretion are similar, also, in 

 their obscurity : there is the same difficulty in saying why, 



