12 PHYSIOLOGY CHAP. 



in the vesicle. Later workers have tried by various modes of 

 staining to determine the nature of the epithelial secretions and 

 the paths by which the secretion penetrates the lymphatics. In 

 this connection Langendorff s results are very interesting. He holds 

 that the protoplasm of the colloid cells degenerates, passing into 

 the secretion along with the nuclei, and leaving stellar interstitial 

 spaces between the principal cells, through which the secretion 

 passes freely into the lymphatics (Fig. 6). When the vesicle is 

 emptied its epithelial cells close up again, and once more present 

 a complete cavity, which in its turn forms outlets for the secretion 

 by the above process. In the lymph channels the secretion is 

 diluted by gradual admixture with the lymph, which carries it 

 away to the circulation. 



FIG. 6. A, Segment of thyroid follicle from puppy. (Langendorff.) Treated with Friedlander-Zeiss 

 osmic-haematoxylin method, homogeneous immersion. Numerous cells are seen in colloid 

 degeneration, distinguished from the principal cells by their dark colour. B, same preparation. 

 Superficial view of principal cells and colloid cells. The colloidal cells adhere together to form 

 a network ; they are attenuated, with occasional nuclei, which are flattened and stain more 

 deeply than those of the principal cells. 



According to Lewandowsky, as stated above, the secretion of 

 the vesicular epithelium is not the colloidal substance but a 

 mother substance, from which the colloid is formed. It is, he 

 says, the mother substance that passes into the lymph or blood 

 vessels. But the passage of true colloidal substance from the 

 vesicle into the lymphatics has never been proved, while on the 

 other hand it is not uncommon for a colloidal substance to form in 

 the lymph spaces. 



There are no glandular spaces in the parathyroids analogous to 

 the vesicles of the thyroid. We must therefore conclude that the 

 secretions from the epithelial cells are absorbed in the lymph 

 channels as fast as they are formed. The observations of Mazziotti 

 and Capobianco (1899), particularly those on the parathyroids of 

 the cat, give interesting details in this connection. They find that 

 the blood-vessels which irrigate the epithelial cells contain a 



