STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 35 



The major components of DNA, base, deoxyribose, and phosphoric acid 

 group can therefore be visualized by the ultraviolet absorption teclmique, 

 Feulgen reaction, and basophiha staining, respectively. Only the nucleus 

 gives tests for all three of these constituents. The cytoplasm, usually con- 

 taining only RNA, does not give a Feulgen reaction, with a few rare excep- 

 tions, such as the kinetosome of some protozoan flagellates. The discovery 

 of Feulgen-staining bodies in the cytoplasm is usually taken to suggest the 

 presence of a microbial parasite or symbiont within the cells examined, 

 although an apparently negative reaction can not be taken as proof positive 

 of the absence of infecting microorganisms (Trager, 1952). The Kappa par- 

 ticles of Paramecium were first observed by means of the Feulgen technique 

 (Freer, 1948), which facilitated a direct study of the kinetics of multiplication 

 of this particle within its host. The existence of cytoplasmic inclusions con- 

 taining DNA in human rectal poljrps has been taken to suggest a viral 

 etiology for these lesions (Leuchtenberger, 1954). On the other hand, a 

 cytological confusion of mitochondrion or symbiont within some cells, as in 

 iusect tissues, can usually be resolved on this basis since mitochondria lack 

 DNA. 



In resting nuclei, as indicated above, lack of condensed chromatin may 

 lead to a very faint Feulgen reaction. It has been claimed that the nucleus of 

 the oocyte of the sea urchm does not give an appreciable reaction for DNA, 

 and, therefore, that this nucleic acid is absent from the egg prior to fertiliza- 

 tion (Marshak and Marshak, 1953). However, many workers have taken the 

 position that very faint Feulgen reactions can be seen in these nuclei, and 

 that DNA is reaUy present (Brachet and Ficq, 1956). 



A positive basophilic reaction, marked ultraviolet absorption, negative 

 Feulgen test, and red stain with pyronine suggest the presence of RNA in 

 nucleoh and cytoplasm. To prove the presence of this nucleic acid, we can 

 also introduce the method of difference. Several techniques may be used to 

 remove RNA from cell structure; these include specific solubiHzation under 

 rigorously controlled conditions with ribonuclease, dilute alkaH, or perchloric 

 acid m the cold. The loss of ultraviolet-absorbing capacity or basophilia is 

 evidence for the prior presence of RNA in the structure. This technique was 

 first used to demonstrate RNA in bacteria (Dubos and Thompson, 1938; 

 Dubos and Macleod, 1938) and was then extensively exploited by 

 Brachet. 



It should be noted that before McDonald (1948) devised a technique of 

 freeing ribonuclease from proteolytic contaminants, even crystalline prepara- 

 tions of the enzyme contained such impurities (Cohen, 1945; Schneider, 1946). 

 The use of such preparations in cytological work opens the way to possible 

 error, although recent results with purer enzyme preparations (Kaufmann 

 et al., 1951) have been concordant with the older findings. 



