THE PATHOLOGICAL ANATOMY 



279 



active hyperplasia. This variability is best explained by variations in 

 the blood supply as has been demonstrated experimentally in the regenera- 

 tion following partial removal. Bibbert (c), Boussy and Clunet (&) (c) 

 (d), Virchow (&). 



Involutionary or Recovery Stage. The growth of a secondary 

 hyperplasia may be arrested at 

 any stage of its development and 

 partially or completely return to 

 the colloid or resting state again, 

 just as in the case of the primary 

 hyperplasias. The anatomical 

 changes in this process are again 

 the reverse of those seen in the 

 developmental stage and identical 

 with those outlined under "Involu- 

 tion of Primary Hyperplasias." 

 The involutionary changes, how- 

 ever, are not so easy of recognition 

 nor so easily interpreted because of 

 the frequency of the several com- 

 plications ahovo mpntionprl to Fi ' 15t Exhaustion atrophy,- thyroid 



of bony fish (SalveliniiB fontinalis). This 



particular fish had a large goiter and the 

 figure is the representative picture of its 

 microscopic appearance. Note the marked 

 fibrosis, the compressed and distorted 

 alveoli. The epithelium is high, columnar 

 and irregular. (After Marine and Len- 

 hart, J. Exper. Med., 1910: 12.) 



which the thyroid is so liable. 

 MacCallum (&). 



Exhaustion Atrophy. The 

 secondary hyperplasia may un- 

 dergo involution and recovery 

 which is the common mode of 



termination, or, it may go on to exhaustion atrophy if the hyperplasia is 

 permitted to continue without a period of physiological rest. The series of 

 changes are similar to those already described as occurring in the exhaus- 

 tion stage of primary hyperplasia. Obviously it is even less frequently 

 observed because of the greater amount of thyroid tissue with which to 

 compensate. Simmonds (c), Werdt (a), Wilson, (a) (6) (c). 



Regeneration 



(Compensatory Hyperplasia) 



Kegeneration and simple or spontaneous hyperplasia of developing 

 goiters are identical anatomically and probably physiologically. The thy- 

 roid gland is one of the best adapted of mammalian tissues for the study of 

 regeneration. If any differentiation between regeneration and spontaneous 

 hyperplasia were possible it would be to restrict the term regeneration to 

 the cell growth following the partial removal or partial destruction of the 



