VASCULAR OR DUCTLESS GLANDS. 143 



after being poured into the blood, influence in varying degrees and ways 

 physiological processes, yet the term in this connection will be applied only 

 to the secretions of the thyroid gland, hypophysis cerebri, and adrenal 

 bodies. 



Thyroid Gland. The thyroid gland or body consists of two lobes situated 

 on the lateral aspect of the upper part of the trachea. Each lobe is pyriform 

 in shape, the base being directed downward and on a level with the fifth or 

 sixth tracheal ring. The lobe is about 50 mm. in length, 20 mm. in breadth, 

 and 25 mm. in thickness. As a rule, the lobes are united by a narrow band 

 or isthmus of the same tissue. In color the gland is reddish, and it is abund- 

 antly supplied with blood-vessels and lymphatics. 



Microscopic examination shows that the thyroid consists of an enormous 

 number of closed sacs or vesicles, variable in size, the largest not measuring 

 more than o.i mm. in diameter. Each sac is composed of a thin homo- 

 geneous membrane lined by cuboid epithelium. The interior of the sac in 

 adult life contains a transparent viscid fluid, containing albumin and termed 

 "colloid" substance. Externally, the sacs are surrounded by a plexus of 

 capillary blood-vessels and lymphatics. The individual sacs are united and 

 supported by connective tissue, which forms, in addition, a covering for the 

 entire gland. 



The Effects of the Removal of the Thyroid. The knowledge at present 

 possessed as to the function of the thyroid gland, especially in mammals, is 

 the outcome of a study of the effects which follow its arrest of development 

 in the child, its degeneration in the adult, its extirpation in the human being 

 as well as in animals. The results, however, which follow its extirpation 

 are not always uniform in all animals; sufficient reasons for which lack of 

 uniformity cannot always be assigned. 



Cretinism, a condition characterized by a want of physical and mental 

 development, is associated with, if not directly dependent on, a congenital 

 absence or an arrested development of the thyroid, either at the time of birth 

 or during the early years of childhood. 



Myxedema, a condition of the skin in which there is a hyperplasia of the 

 connective tissue, of an embryonic type, rich in mucin, is generally regarded 

 as one of the effects of degenerative processes in the thyroid. Partly in 

 consequence of this change in the skin the face becomes broader, swollen, and 

 flattened, giving rise to a loss of expression. At the same time the mind 

 becomes dull, clouded, even approximating the idiotic type. This supposed 

 infiltration of the skin with mucin was termed myxedema by Ord, who at the 

 same time associated it with a change in the structure of the thyroid as a 

 result of which it became functionally useless. 



