422 USES OF THE LIVER DUCTLESS GLANDS. 



with the surrounding parts. From the internal surface of this membrane, 

 are fibrous bands, or trabeculae, giving off, as they pass through the gland, 

 secondary trabeculae, and then subdividing until they become of microscopic 

 size. By this arrangement the gland is divided up into small, communicat- 

 ing cells. The trabeculae contain many small, elastic fibres. Throughout 

 the substance of the gland, lodged in the meshes of the trabeculag, are 

 rounded or ovoid, closed vesicles, measuring -^ to -^ of an inch (40 to 

 100 fji). These are formed of a structureless membrane and are lined by 

 a single layer of pale, granular, nucleated cells, -5^0- to ^Air ^ an i ncn 

 (8 to 12 //,) in diameter. The layer of cells sometimes lines the vesicle com- 

 pletely, sometimes it is incomplete, and sometimes it is wanting. The con- 

 tents of the vesicles are a clear, yellowish, slightly viscid, albuminoid fluid, 

 with a few granules, pale cells, and nuclei. The vesicles are arranged in the 

 form of lobules, and between them are the great veins. 



Vessels and Nerves. The blood-vessels of the thyroid gland are very 

 abundant, this organ being supplied by the superior and inferior thyroid 

 arteries and sometimes by a branch from the innominata. The arteries 

 break up into a close, capillary plexus, surrounding the vesicles with a rich 

 net-work, but never penetrating their interior. The veins are large, and 

 like the hepatic veins, they are so closely adherent to the surrounding tissue 

 that they do not collapse when cut across. The veins emerging from the 

 gland form a plexus over its surface and the surface of the trachea, and they 

 then go to form the superior, middle and inferior thyroid veins. The nerves 

 are derived from the pneumogastrics and from the cervical sympathetic gan- 

 glia. The lymphatics are abundant but are difficult to inject. The exact 

 distribution of the nerves and the origin of the lymphatics are not well un- 

 derstood. 



What little is known with regard to the chemical constitution of the 

 thyroid gland is embodied in the statement that it contains leucine, xanthine, 

 lactic acid, succinic acid and some volatile fatty acids. The blood of the 

 thyroid veins has been analyzed, but the changes in its composition in pass- 

 ing through the gland are slight and indefinite. It has been asserted that 

 one of the uses of the thyroid gland is to regulate the blood- circulation in the 

 brain, but the observations in support of this view are not very satisfactory. 



Myxmdema. Important facts have lately been developed showing a con- 

 nection between the thyroid gland and a disease characterized by infiltration 

 of the connective tissues with a gelatinous substance containing mucine. 

 This disease has been described by Ord, under the name of myxcedema. It 

 is attended with marked impairment of the mental faculties, and a condition 

 like cretinism. This is usually associated with disease of the thyroid' gland. 



Complete excision of the thyroid gland in the human subject has been 

 followed by the peculiar mental condition characteristic of cretinism. In 

 the lower animals the operation of complete extirpation is fatal. The ex- 

 periments of Horsley, upon dogs and monkeys, show great differences in the 

 results, depending upon age. In young animals- death usually occurs in a 

 few days, while old animals survive the operation four, five, or six months. 



