286 INANITION AND MALNUTRITION 



the details, the typical process appears very similar in all types of inanition, 

 including hibernation and various diseases involving malnutrition. There is a 

 marked decrease in the number of mitoses, but not complete cessation, except 

 perhaps in extreme stages. The number of lymphocytes becomes very greatly 

 reduced, chiefly through emigration into the adjacent tissues and vessels, but 

 partly (especially in later stages) by degeneration of lymphocytes, with phagocy- 

 tosis by the reticulum cells. The reticulum is much more resistant, and assumes 

 a somewhat epithelioid, embryonal appearance, recalling the "reduction" 

 phenomena among certain invertebrates. The reticulum presents a progressive 

 increase in lipoidal content, with degenerative changes in the later stages. 



The atrophy first and foremost affects the cortex, which becomes rarefied 

 by the " delymphoidisation," and lighter than the medulla in stained sections, 

 producing the so-called thymic "inversion." Later the differentiation between 

 cortex and medulla disappears. The Hassall's corpuscles are relatively resis- 

 tant, but also ultimately undergo atrophy and cystic degeneration, and in 

 extreme stages may disappear entirely. 



In contrast with the striking atrophy of the parenchyma, the fibrous stroma 

 is relatively more resistant, and becomes more prominent, giving an appearance 

 of fibrosis or sclerosis in the capsule and interlobular septa. There is usually a 

 prompt disappearance of the ordinary adipose content, thus differing from the 

 typical age involution of the thymus. Although relatively more resistant, the 

 fibrous stroma also decreases progressively in absolute volume, so that in extreme 

 stages the thymus is reduced to a small mass of vascular fibrous tissue, contain- 

 ing only indistinct remnants of the parenchyma. 



Unless the inanition has been extremely severe, there is prompt regeneration 

 of the thymus upon ample refeeding. The remaining cells undergo rapid mito- 

 sis; the reticulum cells regenerate new Hassall's corpuscles in the medulla, and 

 become infiltrated with lymphocytes in the cortical region (as during normal 

 development). Thus the normal structure is ultimately restored, excepting 

 extreme cases where permanent injury may result. 



(A) Effects of Total Inanition, or on Water Only 



The literature upon the "accidental involution" of the thymus has been 

 thoroughly reviewed by Hammar ('o6, '10, '21) and is also included by Biedl 

 ('16, '22). For convenience, the effects of total inanition will be discussed 

 first in the human species; later in the lower forms. 



The earliest observation upon human thymic atrophy was apparently by 

 Verheyen (17 10) who noted its occurrence in persons subjected to strenuous 

 activity ("qui corpus vehementer exercent"). As in the case of most organs, 

 however, the earlier observations upon the human thymus during inanition con- 

 cerned chiefly the weight or size, together with the gross appearance, in various 

 cachectic conditions. Thus Meckel (1810, 1820) observed that the general 

 nutritive condition of the body greatly affects the rapidity with which the 

 thymus atrophies. In a weak, malnourished child of 2 years, he found the 

 thymus "fast ganz geschwunden, saftlos, weich, viel kleiner als bei einem 



