While undergraduates at Caltech, Ken Manly, Mike Anthony and I devised a means of testing the hydrate microcrystal theory of general anesthesia (see S. L. Miller,
In order to test this theory, we needed to make measurements of the potency of various general anesthetic agents at thermodynamic equilibrium and to an accuracy of about 1 to 2%. After a survey of numerous animals, we chose brine shrimp because they were aquatic and could be easily equilibrated with anesthetic; were hearty; were easily grown in large numbers; and were easily controlled by their tendency to swim toward light. Figure 2 illustrates the anesthesia tank we built (along with hatching, purification, and counting apparatus). After hatching and purification, 100,000 to 150,000 brine shrimp were divided between the temperature-controlled separatory funnels and different amounts of anesthetic were introduced into each funnel.
Shrimp that stayed awake swam in the upper, lighted parts of the funnels, while those that went to sleep sank through the stop-cocks into the lower tubes. The separated groups of shrimp were then counted.
Most biological dose-response curves are log-normal as illustrated in Figure 3. When the effect of an anesthetic is plotted vs. the logarithm of the concentration, a normal distribution function is found. This shows that individual variation depends upon a large number of similarly sized independent variables. The dependence upon the logarithm is thought to result from the logarithmic relation between chemical concentrations and the energies of chemical reactions (as in the equation
F = -RT(lnK) from introductory chemistry). 
Figure 4 is a graph of our experimental results for the general anesthetic Halothane (CF
3CClBrH). The logarithm of the anesthetic concentration is plotted vs. the percentage of brine shrimp asleep using a vertical axis such that a normal distribution function will result in a straight line. After introduction of the anesthetic, this line is curved, but it gradually becomes straight as the entire system comes to equilibrium. The straight line allows all of the data from the different concentrations to be used in determining, with high accuracy, the amount of anesthetic required to anesthetize just 50% of the animals.
With this accurate tool for measurement, we were able to distinguish between the then-popular theory of general anesthesia which depended only upon the lipid solubility of anesthetics and the microcrystal theory which depended in predictable ways upon the geometry of specific anesthetic molecules. The microcrystal theory, proposed independently by Miller and by Pauling, turned out to be correct.
This looks like the sort of odd study that provides dark humor con
cerning the waste of tax money - anesthetizing shrimp. Actually, it had fundamental implications for the design of improved general anesthetics for use in human surgery. The entire experiment was conceived and executed by three students during three summer months at a cost of about $2,000 and received no tax financing whatever. It also illustrates the value of statistical distribution functions in solving problems other than analysis of error and statistical significance.Brine shrimp are not yet an endangered species, unlike scientists who work independently of government regulation and control.
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Vol. 22, No. 6
Newsletter: Access to Energy Newsletter Archive Volume: Issues Issue/No.: Vol. 22, No. 6 Date: February 01, 1995 03:32 PM Title: Envy
Copyright © 2004 - Access to Energy Newsletter Archive
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