Sec. 26.6] MAJOR MINERAL METABOLITES 523 



of the Mg 27 was too weak for satisfactory measurement, and therefore no 

 interconversion of the two types of photosynthetic pigments could be 

 demonstrated using this magnesium label. 



Now that the rarer stable species Mg 25 and Mg 26 have been prepared in 

 enriched form, it should be possible to investigate not only the role of mag- 

 nesium in photosynthesis, but also its other known vital functions — in enzyme 

 systems, bone metabolism, cellular permeability, etc. 



26.6. Chlorine. Chlorine, essential as an anion in the higher animals and 

 as a micronutrient requirement for some plants, has three potentially useful 

 radioactive species: the short-lived forms CI 34 (33 min half-life) and CI 38 

 (27-min half-life) and the long-lived form CI 36 (10 6 -year half-life). So far 

 only CI 38 has been used in biological experiments; it. is made in the cyclotron 

 by the reactions Cl 37 (d, p)Cl 38 , Cl 37 (n, t)C1 38 , and K 41 (n, a)Cl 38 . CI 34 can 

 be produced in the cyclotron by two reactions: P 31 (a, n)Cl 34 and S 33 (d, n)Cl 34 . 

 CI 36 , which can be produced in significant amounts only in the nuclear pile, 

 by the reaction Cl 35 (n, 7) CI 36 , has only recently become available for tracer 

 work. 



The short half-life of CI 38 has limited tracer experiments thus far reported 

 for chlorine to short-term studies. When introduced as labeled lithium 

 chloride, CI 38 rapidly finds its way into the chloride space of such organs and 

 tissues as the kidney, liver, muscles, cartilage, and tendons, but not into that 

 of the testes and pyloric mucosa [Oil]. Cl~~ has also been found to penetrate 

 rapidly into erythrocytes [C115]. It appears in normal gastric juice very 

 quickly, within 1 to 2 min after intravenous injection into the man or dog 

 [C12], but more slowly in the case of achlorhydria [C13]. 



When CI 38 is widely available, tracer work with chlorine can be much 

 expanded. 



