48 The Development of the Thymus 
Wallisch (30), 03, measured the volume of the human thymus and of 
the corpuscles of Hassall at various stages. He finds that the total volume 
of the corpuscles of a 7-mo. embryo is 4.6 mm.,’ and of those of a 6-mo. 
child, 174.6 mm.’ The total volume of the thymus of a 78-mm. embryo, 
when it has already been partly transformed into adenoid tissue is only 
6.8 mm.’ Since there is no evidence that the cells of the corpuscles 
multiply, he concludes that they cannot be regarded merely as remnants 
of the original epithelial anlage. 
Disregarding the crude observations of the earliest investigators, there 
remain three distinct theories of the formation of the corpuscles of 
Hassall. 
1. The epithelal anlage of the thymus is broken up by the invading 
mesenchymal elements. The separated masses of epithelial cells undergo 
further changes mainly of a degenerative nature to form the corpuscles. 
This was the belief of His and Kolliker. According to this interpretation, 
the corpuscles are to be regarded as remnants that have nothing further to 
do with the gland. Stieda, Maurer, and Ver Hecke held this view in a 
modified form. Stieda regarded the cells forming the corpuscles as 
epithelial remnants but admitted that they go through a stage in which, 
for a time, they lose their epithelial character. This is substantially the 
same as Maurer’s view. He thinks that the cells of the epithelial anlage 
all become lymphoid, and that some of them afterwards reassume their 
epithehal nature and form the corpuscles. Ver Eecke regards the cor- 
puscles as epithelial remnants but thinks that they are glandular in nature, 
not mere useless remains. 
2. The corpuscles are formed from the proliferating walls of blood- 
vessels. This idea was suggested by Cornil and Ranvier and elaborated by 
Afanassiew. Nusbaum and Machowski accept Afanassiew’s view except 
that they believe the adventitia of the blood-vessels as well as their endo- 
thelium takes part in the formation of a corpuscle. ‘These investigators 
thought that the formation of the corpuscles is connected with the in- 
volution of the thymus. 
3. The corpuscles are formed from reticulum cells of the medulla 
and grow by apposition of the surrounding cells. This view was advanced 
by Ammann. Ammann thought that the reticulum is of connective tissue 
origin. He also believed that leucocytes formed the central part at least 
of some corpuscles. Hermann and Tourneux accepted Ammann’s results, 
except that they ascribed an epithelial origin to the reticulum. (I do not 
know whether they accepted the origin from leucocytes described by 
Ammann.) Ammann thought that the corpuscles formed because of a 
physiological decrease in the rate of growth in the medulla. 
