THE DUCTLESS GLANDS 1245 



central nervous system. Schafer regards the principle giving rise to diuresis 

 as distinct from that causing contraction of unstriated muscle, since diuresis 

 may occur without corresponding rise of blood pressure. The independence 

 of the two phenomena, renal and vascular, cannot be regarded as proved. 



(c) The posterior lobe consists mainly of neuroglia. We have no clue to its 

 functions apart from the masses of intermediate cells which it may contain. 



Very little can be said as to the other ductless glands. The thymus 

 forms two large masses in the anterior mediastinum, which in man grow up 

 to the second year of life and then rapidly diminish, so that only traces 

 are to be found at puberty. It contains a large amount of lymphatic tissue 

 and is therefore often associated with the lymphatic glands as the seat of 

 formation of lymph corpuscles. The epithelial remains of Hassell's cor- 

 puscles found in the medullary part of its globules have not had any function 

 assigned to them. In certain cases of arrested development or of general 

 weakness in young people, the thymus has been found to be persistent. 

 The effect of extracts made from the thymus do not differ from those of 

 extracts made from any other cellular organ. 



The pineal gland has so far not been proved to have any function in 

 metabolism. 1 It is interesting as a vestigial remnant of a primitive dorsal 

 eye. In certain lizards this organ still presents traces of its original structure, 

 and is found to conform to the invertebrate type of eye. It is doubtful 

 whether at any time in the history of vertebrates the pineal eye -has been 

 functional. 



The carotid and coccygeal glands have often been grouped with the 

 collections of chroniafnne cells already described as associated with the 

 sympathetic system. Their structure resembles more nearly that of the 

 parathyroid bodies or the anterior lobe of the pituitary gland. They con- 

 sist of a small collection of columns. or masses of cells bound together by 

 connective tissue with a rich supply of blood capillaries. Nothing is known 

 as to their function. 



The lymph and hsemolymph glands, and the spleen, are often grouped 

 with these ductless glands. The essential activity of these bodies however 

 lies in the production, not of a diffusible chemical substance, but of formed 

 elements e. g. lymph corpuscles, and they do not properly fall within the 

 scope of this chapter. As a matter of convenience, we may deal shortly 

 here with the functions of the spleen. 



THE SPLEEN 



This organ is similar in many respects to a lymphatic gland. It is 

 formed of a framework of connective tissue and unstriated muscular fibres, 

 in the interstices of which is contained the splenic pulp. This consists of a 

 fine fibrillar network, on the fibrils of which lie endothelial cells. The 

 meshes contain the cells of the splenic pulp, which are fairly large polygonal 



1 Cases have been recorded in which tumours of the pineal body have been associated 

 with obesity, premature sexual development and early maturity. 



