102 RHODA ERDMANN 



cytes; store fat; lose their projections and partially vacuolize, as- 

 suming the form of the "cell culture type." 



The network of the bone marrow, having lost its cells, and no 

 longer able to send out emigrating cells, consists of slender con- 

 nective tissue cells. These show a remarkable paucity of 

 chromatin, are strongly acidophil, and possess sieve-like vacu- 

 oles of the finest type. 



The 'Riesenzellen' of Foot comprehend several cell types: 



1. Transformed fat cells and elongated, vacuolized connective 

 tissue cells. 



2. Newly emigrated basophil cells of the bone marrow 

 network, which are related to the ''histiotype Wanderzelle" of 

 Dantschakoff. 



3. Some few myelocytes and flattened out eosinophil mono- 

 or poly-morphonuclear leucocytes. 



These two phenomena, the dying of the cell forms which are 

 not adapted to the continued growth in tissue culture, and the 

 adapting of a new character by those cells which are capable of 

 living longer periods in the plasma medium, often overlaps. 

 They appear more sharply separated in cultures of almost fat- 

 less bone marrow, where few 'Riesenzellen' appear in the first 

 days of incubation. From the third to the fifth day, when the 

 loosening of the bone marrow network and its content has begun, 

 they become numerous. The duration of these periods may be 

 stated as follows : The first period lasts from the first to the third 

 day; the second period from the third day to the death of the 

 culture. The surviving cells of the cell culture type (Foot) are 

 modified fat cells and newly formed wandering cells of the mes- 

 enchymelike type. After fourteen days' cultivation, they are, 

 except the elongated connective tissue cells the only living cells. 

 They belong to the connective tissue cell type and may, when 

 the medium is renewed, grow indefinitely. 



DISCUSSION ANX> CONCLUSIONS 



As one of the first results of our analytic study, let us discuss 

 the fact that the so-called X or 'Riesenzellen' of Foot represent 

 several different cell types. The myelocytes and larger eosino- 

 phil leucocytes acquire, as shown, good dimensions in the tissue 



