2 PHYSIOLOGY CHAP. 



of the tissues and glandular organs. This differentiation between 

 the two kinds of cells arises from the fact that while in the former 

 the exchange of materials with the medium (blood and lymph) 

 is the means, or condition, of the development of other forms of 

 energy, and is subservient to other special functions, in the latter, 

 which are known as "secretory," this exchange is the specific 

 function hence it is more prominent, and assumes a distinctive 

 character. 



From this point of view the physiological concept of secretion 

 is entirely independent of the morphological concept of the gland. 

 In so far as the cells of the lymphoid or adenoid tissues and 

 organs considered in the last chapter have a lymphapoietic and 

 haemapoietic function, they are true secretory tissues and organs, 

 though destitute of glandular structure proper. But they are 

 intercalated along the lymph- and blood-vessels, with which they 

 communicate directly, and into which they pour their cytological 

 and chemical products, while gland, in the widest sense, implies a 

 complex of secreting epithelial cells, which form the walls of cavities 

 that are quite distinct from the lymph- and blood-vessels, and in 

 which the secretion, i.e. the product of their secretory activity, 

 accumulates. 



The physiological study of the adenoid tissues and glands is 

 thus logically succeeded by that of the glandular tissues and 

 organs proper. 



I. Midway in the eighteenth century, Albrecht von Haller, 

 speaking of the functions of the glandular organs, observed : 

 multa in physiologia obscura ; obscurius hac ipsa functione nihil. 

 So long as the structure of the glandular organs was imperfectly 

 known, physiological theories as to the secretory processes were 

 necessarily vague and confused, and highly speculative in 

 character. To cite a classical example : the ancients long held 

 that the pituita, or nasal mucus, was a secretion of the brain, 

 that flowed through the lamina cribrosa of the ethmoid. The 

 error was only corrected in 1660, when Schneider described the 

 mucous membrane which bears his name. 



At the same period the anatomy of the glands was more 

 closely studied by Glisson, Wharton, Wirsung, Stensen, Kivini, 

 Peyer, and Brunner. Malpighi (1665) was the first who 

 investigated their internal structure. He stated that all the 

 glandular ducts terminate in acini (grana glandulosa}, which 

 receive their juices from the minute blood-vessels by which they 

 are surrounded, and that the juices collected within the acini were 

 then poured out through the excretory ducts. 



Kuysch (1696) disputed this theory, and maintained, on the 

 strength of fallacious arguments derived from his celebrated 

 artificial injection of the glandular vessels, that the gland 

 substance proper is also composed of blood-vessels, and that the 



