270 Cc. M. JACKSON 
masses intermingled with the medulla are finally displaced and 
- squeezed out of the medullary mass. In the rat, at least, there is 
no evidence that such a displacement occurs. It appears rather 
that the medulla becomes confluent through degeneration and 
absorption of the intermingled cortical remnants. This process 
is difficult to observe in preparations fixed and stained in the 
usual manner, on which account it is easily overlooked, but it is 
clearly evident in frozen sections stained with Herxheimer’s scar- 
let red. In such preparations, the stained liposomes reveal the 
atrophic cortical cells undergoing gradual atrophy and absorp- 
tion. A careful study of similar preparations would probably 
show that in other forms the primitive cortical strands in the 
medulla likewise undergo degeneration and absorption. 
The process of absorption of the cortical tissue continues during 
the postnatal growth and development of the suprarenal gland, 
associated with the expansion of the medulla. The continued 
postnatal growth of the medulla has been noted in the rat, cat, 
rabbit, and,guinea-pig by Elliott and Tuckett (06) and in man 
by Scheel (’08), Starkel and Wegrzynowski (10), Thomas (’11). 
Kern (711), and others. The continued postnatal increase in the 
absolute volume of the medulla in the rat is confirmed by the 
extensive data in the present study. 
This expansion of the medulla necessarily involves an encroach- 
ment upon the space formerly occupied by cortex. A priori, this 
might happen in three ways: 1. There might be a corresponding 
interstitial growth and expansion of the adjacent cortex. This, 
however, would require continued multiplication and growth of 
the cells in the inner cortical zone, and numerous observers (as 
previously shown) agree that postnatal cell division in the inner 
cortical zone during postnatal growth rarely or never occurs. 
2. In the absence of cell division with interstitial growth, the 
inner cortical zone might remain passive and be mechanically 
displaced by the expansion of the medulla. Such a displacement, 
however, would inevitably result in a very marked flattening of 
the cortical cells on the adjacent surface of the expanding medulla 
It cannot be denied that occasionally such a flattening does ap- 
pear, but it is irregular and inconstant. Indeed the characteristic 
