294 INANITION AND MALNUTRITION 



lymphocytes of the cortex become greatly reduced in number through migration 

 into the surrounding connective tissue, especially around the blood vessels and 

 lymph vessels. There may also be migration into the medulla. The emigration 

 of the lymphocytes leaves the cortical reticulum more prominent and the surface 

 cells may become epithelioid in appearance (as in embryonal stages). The dis- 

 tinction between cortex and medulla is lost, and degenerative changes appear in 

 the remaining cells. There is at least a relative increase in the interlobular 

 connective tissue and the vascular stroma, but it is uncertain whether there is an 

 actual sclerosis, as described especially by the French authors. The myoid cells 

 and Hassall's corpuscles undergo variable, regressive changes, sometimes disap- 

 pearing. In the teleost fish, Labrns rupestris, starved 23-31 days, Hammar 

 ('09) described a reduction to one-sixth in the weight of the thymus, and histo- 

 logical changes similar to those found in higher vertebrates. 



Hammar's pupil, Jonson ('08, '09), made a series of accurately controlled 

 experiments upon young rabbits on acute inanition (water only) or chronic 

 underfeeding (maintenance of constant body weight) ; also a series refed after 

 inanition. In 4 weeks of chronic inanition, the thymus weight decreased to about 

 ^0 and the parenchyma to about ^'65 of the normal. In 9 days of acute inani- 

 tion, the thymus was reduced to 34 an d the parenchyma to 34 normal weight. 



Of the parenchyma, the cortex suffered the greatest reduction — to 342 in 2 

 weeks of underfeeding and to % in 5 days of acute inanition. In later stages the 

 cortex has usually disappeared. The cortex atrophies chiefly by emigration 

 of the lymphocytes into the lymph spaces (and veins?). The persistent reticu- 

 lum cells gradually assume an epithelioid appearance, undergoing degenerative 

 changes only in the later stages. The number of mitoses in the entire thymus 

 was reduced from 28,500,000 to 6,500,000 in 4 days of acute inanition, and from 

 10,500,000 to 3,100 in 4 weeks of chronic inanition. The persistent mitoses 

 were chiefly in the reticulum cells. Hassall's corpuscles showed a varied resis- 

 tance. The unicellular forms disappeared (by simple atrophy?) even in the 

 second week of underfeeding, while the multicellular corpuscles were reduced 

 (partly by degeneration) from 139,200 to 16,100 in 4 weeks. During acute 

 inanition, the unicellular forms decreased from 170,000 to 44,000, and the 

 multicellular from about 741,500 to 352,700. The interstitial (fibrous) tissue 

 was reduced to about % normal weight in 4 weeks of underfeeding; with a 

 smaller loss in acute inanition. The interstitial fat is completely resorbed, 

 and the interstitial fibrous tissue assumes a loose, edematous appearance. 



Jonson's refed rabbits made a rapid recovery, showing a distinct increase in 

 the weight of thymus and parenchyma even in 2 days, and nearly normal condi- 

 tions in 3 weeks. "Die Zunahme des Parenchyms wird in erster Linie durch 

 Einwanderung von Lymphocyten aus den Lymph- (und Blut-) Wegen bedingt, 

 wozu friihzeitig eine nicht geringe Zunahme von Mitosen in Lymphocyten und 

 Retikulumzellen hinzukommt." The cortex regenerates first. Differentiation 

 of the typical structure in the medulla, with regeneration of Hassall's corpuscles 

 (by hypertrophy of the reticulum cells), begins only after 2 weeks of refeeding. 

 The interstitial fibrous stroma recuperates rapidly, and fat cell groups begin to 

 appear even after 2 days of refeeding. 



