DAVID MARINE 



of physiological need, persists. The entire gland is invested with an 

 outer fibrous areolar capsule which strips easily, leaving a slightly 



Fig. C. Normal thyroid of common fowl (Gallus domesticus ) . 



lobulated smooth surface. The inner or proper capsule is thin and trans- 

 lucent. Thickened portions of the true capsule (trabeculse) extend into the 

 gland and vaguely mark out the lobules and support the blood and lymph 



vessels. The color of the thyroid is 

 similar in all animals examined and 

 varies from a pale translucent amber- 

 red to a bright amber-red. The con- 

 sistency is firm and somewhat elastic. 

 On section, the larger alveoli can be 

 distinguished with the naked eye in 

 all the larger mammals. They vary 

 considerably in size, although the 

 alveoli of normal thyroids vary the 

 least and measurements of from 0.1 to 

 0.5 mm. would include most of the 

 alveoli of the normal human thyroid. 

 All the alveoli are filled with a glairy 

 amber-colored viscid globulin the so- 

 called colloid which gives to the 

 thyroid its specific characteristic, chemical and physical. This colloid con- 

 tains the active principle of the gland an iodin compound which Kendall 

 isolated in pure form and named thyroxin and it is believed to be the only 

 vehicle for storing this very active substance in an inert manner. 



l''i^'. 7. Normal thyroid of the sheep. 

 (After Marine, Johns Hokpins Hosp. 

 Mull.. 1!M)7: IS.) 



