The stray light which appears in monochromator and microscope can 



be appreciably reduced. Trials on the modél-system to test the apparatus 



must be made. 



The interprétation of results requires an exact knowledge of the 



absorbing substances to be measured in UV-light as well the changes in 

 absorption which occur when they are exposed to other influences (fixa- 

 tion, pH changes etc). 



The fields of application open to UV-photometry are briefly discussed 

 in the second part. Very satisfying results are obtained with this method 

 in the field of genetics. The nucleic acid content of the individual cell 

 can be measured in absolute units. Since both DNA and RNA absorb 

 UV-light, values for DNA are obtained only after treatment with ribonu- 



clease. 



The UV-photometry may shed new light on the significance of RNA 

 for cell division and growth as well as on the function of gland cells, 

 nerve cells and endocrinological organs. Own investigations on the 

 relation between nucleolus and RNA in the adrenal cortex cytoplasraas 

 well as those made on the Langerhans islands of the pancréas may be 

 cited as examples. 



The new method will prove especially valuable in the field of tumor 

 pathology. The possibility of cytodiagnosis with photometry should be 

 given spécial considération. 



Pronounced changes in the nucleic acid-protein metabolism following 

 virus infection hâve also been observed. 



The UV-absorption range of 300—400 m^, in which the thyroid colloid 

 and certain pigments such as the carotinoids and enzymes of the citnis 

 acid cycle évidence absorption hâve received relatively little attention. 

 The first investigations of the lipofuscin-pigment, haemosiderin and 

 melanin are presented hère. 



The areas of apllications for the cytophotometry in biological and 

 médical sciences hâve by no means been exhausted. 



- 21 



