EFFECTS ON THE THYMUS 293 



In a series of about 40 cases (about half of which represent original observa- 

 tions upon Minnesota cases), in which complete data were available, the average 

 loss in thymus weight in atrophic infants has been calculated upon various 

 bases, as shown in Table 2. Thus in comparison with Scammon's norm for the^ 

 corresponding final body weight, the thymus averages 71.8 per cent, below nor- 

 mal for the entire series, or 75.8 per cent below for the Minnesota data alone. 

 Compared with the normal for the maximum body weight reached during life, 

 the thymus weight averages 80.7 per cent subnormal. Compared with the norm 

 for corresponding height, the thymus loss is 80.6 (80.4) per cent; while for age 

 the thymus appears 82.6 (84.4) per cent subnormal. 



The marked depression of the thymus weight in malnourished infants also 

 appears clearly in Fig. 79, a field graph representing all available cases in which 

 the body weight was 20 per cent or more subnormal according to body length, 

 irrespective of the cause of death. The large dots represent original Minnesota 

 data. Out of nearly 300 cases, only 2 appear above normal, and the profound 

 atrophy in nearly all cases is clearly evident. 



Among the animals, the effect of unfavorable environment upon the thymus 

 has long been known. Wharton (1659) found that the strenuous labor to which 

 young oxen were subjected when yoked causes a marked atrophy of the thymus. 

 Gulliver (1842) similarly observed that "in overdriven lambs the thymus will 

 soon shrink remarkably and be nearly drained of its contents, but will become 

 as quickly distended again during rest and plentiful nourishment." 



Friedleben ('58), in addition to the above mentioned observations on the 

 human thymus, starved young puppies for 12 hours, 40 hours and 14 days, 

 respectively, and demonstrated that the thymus atrophied relatively more than 

 the liver, spleen or the entire body. In the longest experiment, the thymus was 

 reduced to a mere trace, while the body lost 45.7 per cent in weight. Manassein 

 ('69) included some data indicating a marked loss in the weight of the thymus 

 in fasting young rabbits, but he makes no comment thereon. 



Hofmeister ('92) pointed out the similarity between the hunger involution 

 of the thymus and that in other lymphoid tissues, and thought there is a relation 

 between this and the blood lymphocytes. Voit ('94) noted, in dog starved 22 

 days, almost complete disappearance of the thymus, which weighed 31 g. in 

 a normal litter control. 



During fasting or hibernation in frogs, Ver Eecke ('99) found a loss of 75 

 per cent or more in the weight of the thymus. The atrophy involves both cortex 

 and medulla. There is a rarefaction of the lymphoepithelial tissue (including 

 the concentric corpuscles), which is more marked in the medulla. Persistence 

 of the connective tissue gives an appearance of pseudosclerosis. 



We come now to the work of Hammar and his co-workers, who introduced 

 more accurate methods of histological analysis, which have contributed largely 

 to the rapid recent progress in our knowledge of the thymus problem in man and 

 animals. Hammar ('05a) first described the changes as found in rabbits and 

 frogs subjected to inanition, and also in pathological cases in animals and man. 

 The rabbit's thymus may lose half its weight in 3 days of fasting. The mitoses 

 decrease rapidly in number (especially in the cortex) and soon disappear. The 



