146 MICROSCOPIC ANATOMY OF THE ORGANS. 



and that the internal secretion is taken up directly by the blood 

 capillaries, which form a thick network around the alveoli. 

 Changes take place both in the epithelium and the colloid in 

 hypertrophy of the gland, and in such cases symptoms show 

 that the internal secretion also is altered, either in quantity or 

 quality, or in both. 



The interalveolar connective tissue brings many blood- 

 vessels, lymphatics, and nerves to the organ. The blood- 

 vessels form a rich capillary network around the alveoli. 



FIG. 104. 



Digested section of a human thyroid (Flint), showing the framework of the gland and 

 the form of the alveoli. (Fixed in Van Gehuchten's fluid, hardened, extracted with ether, 

 and digested with pancreatin, and cleared in glycerin.) 



The framework of the thyroid has been studied by Flint. 

 The gland was hardened and then digested in pancreatin until 

 all cellular elements had disappeared. The main bundles of 

 connective tissue follow the large vessels. More delicate 

 strands form the supporting membranes of the alveoli. The 

 basement membranes stand out clearly, and the form of the 

 alveoli can be made out (Fig. 104). The alveoli are spherical 

 structures, which lie close to one another, and are separated 

 by a very little connective tissue. The basement membranes 



