CYTOCHEMICAL TECHNIQUES FOR NUCLEIC ACIDS 71 



TABLE I 

 The Effect of Fixative Penetration on Feulgen Intensity" 



Feulgen dye bound Standard error 



Liver (Tetraploid nuclei) 



Center of section 



Edge of section 



Sucrose homogenate 



Frozen section 

 Spermatocytes 



Center of section 



Edge of section 



Sucrose homogenate 



" Values in arbitrary units represent means of 15 measurements on formalin-fixed rat nuclei. All tis- 

 sues were from the same animal. 



from the nuclei with higher Feulgen values. It is possible, then, that this 

 fraction, where present, may partially inhibit the Feulgen recation. Lhotka 

 and Davenport*^ found a more intense reaction if tissues were kept 5 min- 

 utes between removal and fixation in picrosulfosalicylic acid. Protein loss, 

 through autolysis, may be responsible for the difference. The increased 

 Feulgen intensity found in early pycnosis of tumor nuclei^- is possibly also 

 due to protein loss. 



Certain tissues are more readily penetrated by fixatives than others. 

 For example, the structure of rat testis fragments enables a more rapid 

 fixative penetration than denser tissue such as liver. Thus under some 

 conditions, where amounts of dye per nucleus are to be compared between 

 two tissues, the error due to penetration may cause misleading results. 

 Fixation is naturally more uniform with adequately frozen-dried or homog- 

 enized tissues, and such treatment may occasionally be necessary where 

 accurate comparisons are wanted. 



The effects of cytological fixatives on Feulgen-stained slides have been 

 discussed by several investigators.^" •^"^•^"^ Most fixatives give adequate 

 results where fixation has not been prolonged, where tissues have been 

 adequately washed, and where strong oxidizing agents, such as 5% chromic 

 acid, have been avoided. 



5. Hydrolysis 



Many workers have described the effects of hydrolysis time on Feulgen 

 intensity.^^'^"'^"^-^"^-^"^ Typical curves are given in Fig. 5 for hydrolysis in 



'«3 H. Bauer, Z. Zellforsch. 15, 225 (1932). 



10* P. F. Molovidov, Proioplasma 25, 570 (1936). 



lo^ T. Caspersson, Biochem. Z. 253, 97 (1932). 



