1334 PHYSIOLOGY 



and posterior lobes, in addition to the production of some substance 

 which is a general excitant for unstriated muscle and produces diuresis, 

 also furnishes a colloid secretion which passes directly into the ven- 

 tricles of the brain and may be assumed to have some influence on 

 the growth or functions of the 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 lym- 

 phatic glands as the seat of formation of lymph-corpuscles. The 

 epithelial remains of Hassall's corpuscles 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 as we know, no functions in meta- 

 bolism. 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 chromophile 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 consist 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 haemolymph 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 sub- 

 stance, 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. 



