280 DAVID MARINE 



gland. Some observers have stated that regeneration following partial re- 

 moval cease! when the gland reaches its normal volume. This is not neces- 

 sarily the case. The amount of thyroid normally needed by the organism 

 cannot be measured quantitatively for the reason that the smallest number 

 of thyroid cells capable of performing the thyroid functions under favor- 

 able conditions of environment and nutrition is much smaller than the 

 number of thyroid cells required by the organism under unfavorable con- 

 ditions. In short, the amount of thyroid depends on the physiological re- 

 quirements of the animal, and this may be altered by a variety of means. 



The histological characteristics of regeneration are identical with those 

 described under hyperplasias. If one removes three^fourths of the thy- 

 roid of a dog or cat and rigid precautions are taken to prevent the animal's 

 coming in contact with iodin, a series of changes takes place characterized 

 by a striking decrease in the iodin store, the disappearance of colloid, an 

 increase in the blood supply and a change in the alveolar epithelium first 

 recognized in the subcapsular zone of the gland, in which the cells change 

 from low cuboidal to cuboidal, to columnar and finally to high columnar 

 with infoldings and plications. The rapidity of the process depends on the 

 known factors of species of animal, age, the amount of gland removed, the 

 presence of iodin and probably on the other factors of the nature of chemical 

 coordination. Regeneration is not necessarily a part of the normal growth 

 of a normal gland, as can be demonstrated in young animals, where the 

 gland increases in size with the growth of the animal without in any way 

 departing from normal chemistry or normal histology. Edmunds (c), von 

 Eiselsberg, Eppinger and Hofer, Halsted (a) (6), Ribbert (a), Roussy 

 and Clunet (d), Loeb (&), Werner. 



Colloid Glands (Goiters) 



The colloid or resting thyroid may be defined as that anatomical and 

 chemical state which is present when an active hyperplasia, primary or 

 secondary, ceases further growth and returns to the condition nearest 

 normal that such a gland can assume. Colloid glands (goiters) are normal 

 physiologically and abnormal anatomically. They differ from the normal 

 gland only in size and in showing the vestiges of previous ' active hyper- 

 plasia. Colloid glands are properly designated involutions or physiological 

 atrophies of hyperplasias, and are capable of all the biological reactions of 

 the normal thyroid in so far as these are at present known. Clinically, 

 just as in hyperplasias, the great majority of colloid glands never reach 

 the stage of clinical detectability. They complete the cycle of cell changes 

 before sufficient enlargement has taken place and without any detectable 

 symptoms. Unfortunately, many writers use the term colloid gland (goiter) 

 as a clinical term synonymous with simple or endemic goiter. This is wrong. 



