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riu- highly imijnned locliiiiqiie of cultivaling tissue cells 

 has made it possible to study several physiological pro- 

 blems liilherlo unassailable. Carrel '»'' develo|)e<l recinlly. 

 as alreadx' described, a new technique by which (he eullure 

 medium may be renewed frequently without any mechan- 

 ical disturbance of the tissues. With this techni(|ue. epi- 

 thelial cells, fibroblasts and leucocyte's may be observed in 

 a condition of uninterrupted growth for about a month. 

 Therefore tlu' projierties of the leucocytes could now be 

 investigated. 



It was observed that tlu' leucocytes cultivaletl in the 

 special flasks mentioned already, secreted substances which 

 was found to promote mnltiplication of fibroblasts and epi- 

 thelium. When small amounts of foreign protein was added 

 to the culture medium, the Icucocytic secretions acquired 

 a still greater growth-promoting power. It is shown by 

 Carrel^*) that leucocyte^s .secrete growth-promoting sub- 

 stances as well in ^itro as in vivo. C a r r e 1 has called the 

 leucocytes trephocytes i. e. nurses of the fixed cells, 

 as they secrete the tre phones. The leucocytes are found 

 to synthesise growth-promoting substances from certain con- 

 stituents of serum - a process, which fibroblasts or epi- 

 thelial cells are not alile to imitate. This is demonstrated 

 by Carrel in his beautiful experiment in keei)ing colonies 

 of fibroblasts and leucocytes in large flasks in plasma only. 

 After a few days the colony of fibroblasts appeared very 

 degenerated and were almost dying. The colonies of leuco- 

 cytes soon increased in size and reached the outline of the 

 colony of dying fibroblasts. Immediately after the fibro- 

 blasts were reached by the leucocytes, they became re- 

 juvenated. 



An important contribution to the physiology of the tissue 

 cells is here given by C a r r e I. since he has proved the 

 old conception of Claude Bernard that the internal 

 secretions are nutrient, secretions such as glycogen, albumin 

 and fibrin. Claude Bernard and later Renaut con- 



