REFERENCES 15 



the hazard in the use of enzyme preparations that the loss of a stained sub- 

 stance from a cell has been produced by some enzyme action other than 

 that which it was intended should occur. 



2. Even if one neglects the hazard of contamination by other enzymes, 

 there are considerable difficulties in interpreting the removal of sub- 

 stances from sections by enzyme action. For example, it is possible that a 

 structure composed mainly of nucleic acid could be protected from the 

 action of the enzyme ribonuclease by quite small quantities of protein. 

 Even a monolayer of protein might be sufficient to prevent access of the 

 enzyme to its substrate. Conversely, a structure consisting almost entirely 

 of protein, but held together and held in the section by a fine matrix of 

 ribonucleic acid, might well be removed by ribonuclease although the 

 nucleic acid constituted an extremely small fraction of the structure as a 

 whole. 



3. Many of the components even in a fixed preparation are not totally 

 indiffusible and will migrate from the fixed section if a suitable adsorbing 

 reagent is available. For example, Catcheside and Holmes have shown 

 that ribonucleic acid may be removed from chromosomes by what ap- 

 pears to be egg albumin, supposedly an inert protein. 



REFERENCES 



Bauer. 1933. Zeit. /. mikr.-anat. Forsch., 33, 143. 

 Brachet. 1940. C. r. soc. biol. Paris, 133, 90. 



1944. Embryologie chimique (Masson, Paris). 

 Callan. 1952. Symp. Soc. Exp. Biol, 6 (in press). 



Caspersson. 1950. Cell Growth and Cell Function (Norton, New York). 

 Catcheside and Holmes. 1947. Symp. Soc. Exp. Biol, 1, 225. 

 Chayen. 1952. Symp. Soc. Exp. Biol., VI (in press). 

 Danielli. 1946. Nature, 157, 755. 

 Dounce. 1948. Personal Communication. 



Fetjlgen and Rossenbeck. 1924. Zeit. }. physiol. Chemie, 135, 203. 

 Fischer. 1899. Fixierung, Farbung und Bau des Protoplasmas (Gustav 



Fischer, Jena). 

 Fox and Danielli. 1941. Biochem. J., 35, 13, 88. 

 Hardy. 1899. J. Physiol, 24, 158. 

 Holter. 1946. Nature, 158, 917. 



Lison. 1936. Histochimie Animate ^(Gauthier-Villars, Paris). 

 Mugard. 1953. Quart. J. Micros. Sci. (in press). 

 Shapiro. 1939. Cold Spring Harbor Symposia, 8, 406. 

 Stedman and Stedman. 1943. Nature, 152, 267. 



