/ sah This was due to the fact that previous work with ordinery conventional laboratory precedures had built up evidence of which was internretec upon static conditions, of reference were few and based on iong time intervals. with the advent of radioactive isotope multiple samples could be done with preat ease and ccnsiderable accuracy. spread compurison of organ contents could be insice. ~~ sodium belance in the body. Points ‘ide- As a good illustration iet's take For a leng time there was consicereble mystery as to what happened to the sodium chloride. You can make measurements of sodium chloride in the plasm of the human or of tne dog or other animals and you find that it fiuctuates from moment to moment, from hour to huur, and from day to day. Ht took a long time to realize that there were tides in the bleed and in the interstitial tissue and in the storehouses of the bedy which reflected the status of the fluid belance in the body and the needs, Under great demand such us gacecsive sweating the sodium chleride could be pulled out ec. the Storcheuses a.d tht racio-sodius located in ene of the hither to overlooked storehoussS, mancly the bone. The bene esrries abcut twenty ver cent of the sait resident coed ed fron tiic to time. WN 5 a fe & co fu 5 +3 QO oO cr bos fe co 4% of the aveilability of the bone to store things The bone was ordinarily thought of as a fixed structure mainly designed for neisht bearing. meteis but they were there tc stuy.s It was nnewn te fix certain poisonous The bone is a great sponge for some substances. is a esleium appetite mineral with e wide molecular lattice ork. It+ In that lattice work tan be stored easily--stored and rencved—substences which are used in the day to day setivity of the body. If you don't have this dynamic concept of change then the findings which you will obtain in the useof isotope techniques will be entirely unexplainable or confusing. How many sample s~shew many roints—do you need to fix a relationship. That is a very difficult problem and can only be settled by a proper statistical approach. You might need as many as 100 peints, or you might need only five omen. There has been a great deal of useful work done up to now with isotopes in which trends have been indicated fron experiments carried out with three to four anelyses; ut a point on time interval, 2