THE COMBINED 



FLUORESCENCE-PHASECONTRASTMICROSCOPY 



AS A METHOD OF INVESTIGATION 



IN THE PROCESS OF PHAGOCYTOSIS 



D. WITTEKIND 



Medizin. Univ. Klinik, Heidelberg 



The close combination of phase-contrast with fluorescence-mi croscopy 

 has proved valuable in experiments on living cells. Phasecontrast-micro- 

 scopy, demonstrating only the optical qualities of an object, will be use- 

 fully completed by fluorochroming structures, e.g. by using a staining 

 method. After a short explanation of constructive features of the combined 

 microscope its qualification for recognising cell viability will be demon- 

 strated with phagocytes as an example. The question is discussed of 

 how ingested material may influence the way in which phagocyting cells 

 are shown in fluorescence- and phase-contrast microscopy. The possibility 

 is stressed of suspending living cells in concentrated isotonic protein 

 solutions (f. i. albumin and globulin). When the protein content is suffi- 

 ciently high, the cell will appear in négative phase-contrast. For keeping 

 the cell interior in négative phase-contrast the cell membrane must ne- 

 cessarily remain imperméable for substances of high molecular weight. 

 Thus an additional and valuable hint on cell viability is given: Conserva- 

 tion of négative phase-contrast being no reliable criterion of a living cell, 

 a change to positive phase-contrast is not consistent with cell viability. 

 The appearance of living cells is compared with that after fixation and 

 use of staining methods, as a contribution to the question of how certain 

 intravitally observed structures are résistent to histochemical procédures. 



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