Histolot^ical Appearances of the Mammalian Pituitary Body 151 



like the so-called colloid material, and may be of that nature ; but is unlike 

 in many respects the colloid of the thyroid gland. In the posterior lobe 

 of the dog's pituitary somewhat similar appearances present themselves, 

 but in this case the epithelial islets frequently consist of a number of cells 

 which group themselves round a central cavit}^ containing colloid material. 

 Isolated cysts, the walls of which are composed of a single layer of cells, 

 are not uncommon, and were noted by Loth ringer. In the dog, too, the 

 larger cysts of the epithelial investment are not always complete, and the 

 contained material may abut against the neuroglial tissue. The colloid 

 substance, when completely or partly enclosed by epithelial cells, varies 

 considerably in its staining properties in different parts of the same 

 pituitary. As a rule it takes on little depth of colour with stains, and 

 is unlike the colloid of the thyroid in this respect ; it has a hyaline rather 

 than a colloid appearance. Occasionally, however, the substance is denser 

 and takes on a deeper stain, and in the dog sometimes looks as though it 

 were a swollen cell with disintegrating nucleus. The hj'aline material of 

 the nervous portion of the posterior lobe also varies in appearance, and 

 in its staining properties ; most of it might be of the same nature as the 

 so-called colloid of the epithelial investment and of the intermediate part 

 generall}^, but in a diluted form. Some of this material must be the 

 product of the epithelial cells, for it occurs in places where no other kind 

 of cell is present. The universal occurrence of this material in the nervous 

 substance, often at considerable distances from epithelial cells, is difficult 

 to explain, unless we can suppose it to be carried from them by lymphatic 

 vessels. The substance often does lie in distinct spaces lined by w^hat 

 appears to be endothelial cells. The general tendency of the direction of 

 the material seems to be towards the neck of the infundibulum in the cat, 

 and it increases in amount towards this situation. Large masses are some- 

 times seen lying among the ependyma cells, and similar material ma}^ be 

 present in large amount in the central cavity, connnunications between the 

 two being evident in places. 



In fig. 15 a typical portion of the neck of the infundibulum of a cats 

 pituitary is seen. The central cavity is lined by ependyma cells, outside 

 whicll are cells with large nuclei and little proto])lasm. Occupying the 

 central cavity is a mass of hyaline material, and masses of a similar 

 substance lie beneath the ependyma cells and between the ependyma 

 fibres. In other places in the posterior lobe the material is distinctly 

 present in lymph channels accompanying the blood-vessels. Evidence 

 strongly points to the probabilit}' that the material is on its way to the 

 central cavity, and so into the ventricles of the brain. In this sense the 

 posterior lobe of the pituitary is a gland which pours its secretion into the 

 third ventricle of the brain. It is possible that the ependyma and neuroglia 

 cells have also a secretory function, but improbable that they secrete tlie 

 material described. They may, however, have some influence upon it. 

 The most likely supposition is that the ependyma and neuroglia cells 



