THYMUS GLAND. 423 



As far as could be ascertained from these experiments upon the lower ani- 

 mals dogs and monkeys the conditions, including the mental phenomena, 

 resembled those observed in cases of myxoedema in the human subject, The 

 animals operated upon were found to be exceedingly sensitive to cold. If put 

 in a hot-air bath at a temperature of 105 Fahr. (40-5 C.) after the general 

 symptoms made their appearance, the animals could be kept alive for several 

 months. Horsley described the symptoms in monkeys, after three to seven 

 weeks, as " commencing hebetude and mucinoid degeneration of the connect- 

 ive tissues," and after five to eight weeks, " complete imbecility and atrophy 

 of all tissues,"especially muscles." 



It is difficult to draw, from these observations, absolutely definite conclu- 

 sions with regard to the physiological relations of the thyroid gland. This 

 organ seems essential to life, and its removal profoundly affects the general 

 processes of nutrition. It influences the quantity of mucine in the body, but 

 precisely in what way, it is difficult to determine. 



THYMUS GLAND. 



In its anatomy the thymus resembles the ductless glands, but its office, 

 whatever this may be, is confined to early life. In the adult the organ is 

 wanting, traces, only, of fibrous tissue with a little fat existing after puberty 

 in the situation previously occupied by this gland. As there never has been 

 a plausible theory, even, of the uses of this organ, the existence of which is 

 confined to the first two or three years of life, it seems necessary only to give 

 a brief sketch of its structure. 



The thymus appears at about the third month of foetal life and gradually 

 increases in size until about the end of the second year. It then undergoes 

 atrophy and it disappears almost entirely at the age of puberty. It is situ- 

 ated partly in the thorax and partly in the neck. The thoracic portion is in 

 the anterior mediastinum, resting upon the pericardium, extending as low as 

 the fourth costal cartilage. The cervical portion extends upward as far as the 

 lower border of the thyroid gland. The whole gland is about two inches 

 (50-8 mm.) in length, an inch and a half (38 mm.) broad at its lower por- 

 tion, and about one-quarter of an inch (6'4 mm.) thick. Its color is grayish 

 with a slightly rosy tint. It is usually in the form of two lateral lobes lying 

 in apposition in the median line, although sometimes .there exists but a 

 single lobe. It is composed of a number of lobules held together by con- 

 nective tissue 



The proper coat of the thymus is a delicate, fibrous membrane sending 

 processes into the interior of the organ. Its fibrous structure, however, is 

 loose, so that the lobules can be separated with little difficulty. Portions of 

 the gland may be, as it were, unravelled, by loosening the interstitial fibrous 

 tissue. In this way it is found to be composed of little lobular masses at- 

 tached to a continuous cord. This arrangement is more distinct in the in- 

 ferior animals of large size than in man. The lobules are composed of 

 rounded vesicles, ten to fifteen in number, and T j to ^ of an inch (20ft 

 to 600 //,) in diameter. The walls of these vesicles are thin, finely granular 



