TECHNIQUES OF ANATOMY — ROOFE AND LESHER 333 



cases to measure quantitatively chemical substances within the cell 

 itself without radically changing it. It is this phase of cytology with 

 which we shall now deal. 



CYTOLOGICAL AND MICROSCOPICAL TECHNIQUES 



Enzymes, proteins, nucleic acids. — Northrup (1949) in his discus- 

 sion on "Enzymes and the Synthesis of Proteins," emphasizes the close 

 relationship which exists between enzymes, proteins, and viruses. 

 Nucleic acids obviously fit into the same picture whether one con- 

 siders them from the standpoint of a conjugated protein, i. e., the 

 nucleoproteins, or as enzymes. It has been suggested that the nucleic 

 acids may, acting as coenzymes, funnel energy into metabolic actions. 



Chemically, cellular components vary, depending upon the func- 

 tion of the cell and the physiological condition of the main tissue mass 

 of which the cells are a part. Despite this chemical variability, the 

 nucleic acids are always present as one of the fundamental compo- 

 nents. It is now well established that two types of nucleic acids 

 exist, ribonucleic acid and desoxyribonucleic acid. The two are to 

 be found in both plant and animal cells. Kibonucleic acid is con- 

 centrated for the most part in the cytoplasm and the nucleolus, desoxy- 

 ribonucleic acid in the chromosomes. The organization and perfec- 

 tion of histochemical and cytochemical methods for the detection and 

 measurement of nucleic acids at a microscopic level, have stimulated 

 an intensely renewed interest in the nucleoproteins and their pros- 

 thetic groups, the nucleic acids. 



Recent investigations have shown that nucleic acids are involved in 

 many vital cell functions. Desoxyribonucleic acid (DNA) condenses 

 on the chromosomes during division, at which time it becomes ap- 

 parent that a new gene chain has been or is being synthesized. There 

 is, furthermore, an apparent high concentration of ribonucleic acid 

 (RNA) in those tissues active in protein synthesis (secretory glands, 

 embryos, tumors, etc.). Such self -duplicating bodies as viruses and 

 plasmagenes, both of which may be closely related to genes, have 

 proved to be nucleoprotein in nature. In Muller's (1950) opinion the 

 genetic material itself, that is the gene, is a nucleoprotein, but he as- 

 sumes that the difference between genes, like the specificity between 

 enzymes, lies chiefly in the protein and not in the nucleic acid. 



The most impressive technique devised for the identification, local- 

 ization, and possible measurement of the two nucleic acids is that 

 by Casperson (1936), the ultraviolet absorption method. Casperson 

 (1950) describes in detail the apparatus and procedures in his new 

 book, "Cell Growth and Cell Function." Between 2500 and 3000 A. 

 the absorption of the cell is usually dominated by that of the nucleo- 

 tides and proteins. This broad band can be further broken down to 



