PROCEDURES FOR INDIVIDUAL RADIOISOTOPES 203 



(detn.), whereas others were derived from the relationship between 

 measured aluminum absorption data and self-absorption values (calc.). 



Data on the critical organ, body burden, air concentration, and water 

 concentration were taken from National Bureau of Standards Handbook 52 

 (2). The maximum permissible body burden is given in microcuries (mc), 

 and the maximum permissible concentrations in air and water for contin- 

 uous exposure are given in microcuries per milliliter (^c/ml) of air and 

 water. The effective half-life {Effect. Ty^ takes into account both the 

 physical and biological half-lives. 



Under Intake Levels there is first given an indication of the normal 

 intake for the animal and plant so that the investigator can estimate 

 from the specific activities available, the sensitivities of measurement, 

 and probable uptake whether it will be possible to use physiological 

 dosages. Much of this information was taken from standard texts, 

 particularly Monier-Williams (3), Maynard (4), and Farris and Griffith 

 (5). Nutrient-solution data were calculated from Hoagland's recom- 

 mendations, as given in Curtis and Clark (6), and the composition of crop 

 plants taken from Beeson (7). It is also useful to know the amounts of 

 the element which will cause injury, and such data were, in general, 

 available from Sollmann (8), Fairhall (9), and Farris and Griffith (5). 

 Toxic levels are usually given in terms of milligrams per kilogram of body 

 weight (mg/kg). 



The discussion under Radioassay is concerned first with the advantages 

 or disadvantages of various preparations when more than one are avail- 

 able. An indication is given as to suitable methods of counting and 

 especially any difficulties when these are known to occur. 



Methods for chemical estimation are outlined because very often they 

 give information as to techniques that are useful even when only radio- 

 assay is required. With biologically important elements, both chemical 

 and radioactivity estimation is frequently required to permit turnover 

 calculations. Where the information is available, the suitability of the 

 various ashing methods has been mentioned. 



Under the heading Typical JMethods an attempt has been made to 

 outline procedures that have actually been used in experimentation. The 

 amount of radioactivity used in the system is listed to give an idea of 

 dosage requirements. The procedures are described for handling the 

 samples and making the counts, especially where variations or convenient 

 techniques have been used. Where possible, examples have been given 

 from both plant and animal studies. Although animal experimentation 

 appears to predominate, it should be pointed out that sample-handling 

 procedures are usually quite similar for both animal and plant tissue. No 

 attempt has been made to give results obtained, since the emphasis is 

 upon procedures. 



