203 



sidcrcd the leucocytes as cells playing a capital role as 

 mobile unicellular glands, carrying the food material to the 

 fixed cells, .loll y concluded ti'om his investigations on the 

 lymphoid apparatus that lym|)hocyles store im|)ortMnl che- 

 mical substances, which are used by the organism. 



The existence of such substances is now demonstrated by 

 Carrel, who called them trei)hones, and they are defined as 

 substance.^ which are used by the cells directly for the 

 synthesis of their protoplasm. On the contrary, the hor- 

 mones are defined as substances which stimulate olher cells 

 to activity. They act as catalysts, but do not build up pro- 

 toplasm. Both trephones and hormones are required for the 

 growth of tissue. 



It has often been mentioned in this book that tlie normal 

 tissue cells, fibroblasts and epithelial cells are not able to 

 sj^nthesise their jjrotoplasm from the serum constituents. 

 They require substances called trephones, which are present 

 in embryonic tissue, certain glandular tissue and in the leuco- 

 cytes; the latter being able to synthesise these substances 

 from the serum compounds. Fibroblasts and epithelial cells 

 are maintained in a true state of cultivation only when 

 embryonic tissue juice is added to the culture medium. 

 Lymphocytes and large mononuclear and certain malignant 

 tissue cells behave in entirely different manner. According 

 to C a r r e 1, the monocytes die in a short time when cultivated 

 in embryonic tissue juice. In diluted serum they remain 

 alive for a mucli longer ])eriod of time. It is clear tnat they 

 build up protoplasm from some of the compounds of serum, 

 a thing which fibroblasts and epithelial cells are unable to 

 do. Fibroblasts cultivated in a medium containing embryonic 

 tissue juice as the only source of nitrogen multiply exten- 

 sively. In the latter case, there is no doubt that *the em- 

 bryonic juices do not act as hormones, but actually take 

 part in the synthesis of protoplasm. 



The conclusion of Carrel's investigation according to 

 Carrel himself is, that the lymphocytes both possess 



