K. T. Bell 49 
My own observations on the development of the corpuscles of Hassall 
in pig embryos, will now be considered. The medulla, as previously de- 
scribed, begins to form from the epithelial syncytium usually near the 
center of the lobule. It is first recognized by its more marked reaction 
with cytoplasmic stains such as Congo red. Shortly after the medulla 
begins to form, the earliest stages of the corpuscles may be observed. - A 
few corpuscles have appeared at 9.5 em. I did not find them earlier. 
They are all formed from the epithehal syneytium of the medulla. 
Before beginning this discussion I will explain the use of my terms. 
By a corpuscle of Hassall, I mean a modified area of the epithelial syn- 
cytium of the medulla, containing at some period of its development, one 
or more nuclei, and-whose cytoplasm has been in part or entirely trans- 
formed into colloid. The term colloid is applied to various substances 
probably of widely different chemical nature, but is fairly adapted to our 
imperfect knowledge. I shall use the term here in the restricted sense 
employed by Ziegler,’ i. e., hyaline substances of epithelial origin, that do 
not give the reactions of mucin. 
Colloid in the corpuscles of Hassall does not usually appear as solid 
masses in its early formation, but as fibers, granules, or sheets which are 
separated by more or less cytoplasm that is not yet changed. This stage 
I have called, “ colloid in formation” (c f). It later assumes a more 
solid homogeneous appearance which I call solid colloid (¢ s). Often 
the solid colloid stains intensely with cytoplasmic stains. 1 call this 
kind solid deeply-staining colloid (¢ s d). In later stages, the colloid 
often loses its affinity for cytoplasmic stains, staining a very pale color or 
not staining at all. I call this variety old colloid (0c). 
According to their mode of development, the corpuscles of Hassall may 
be classified as follows: 
A. Concentric Corpuscles. 
a. Simple. 
1. Ordinary type. 
2. Hpithelioid type. 
3. Cystic type. 
b. Compound. 
B. Irregular Corpuscles. 
a. Compact type. 
b. Reticular type. 
*Gen. Pathology, 10th ed., Warthin’s translation, p. 205. 
