1 2 3 4

		Discussion      As predicted, the hearts beat faster in DMEM than in HR; this is pobably due to the presence of glucose as an energy source in the DMEM. Also consistent with our expectations, dilute caffeine solutions (0.1 mg/ml and 0.2 mg/ml) did further increase the heart rates relative to the base rate (see table 3). However, we did not expect that higher dosages of caffeine (0.3-1.0 mg/ml) would increase the heart rates to a lesser extent than the lower concentrations of caffeine and eventually cause the hearts to stop beating (see figure 11). Table 3. The average number of beats per minute in each solution produced by all the hearts (groups A and B). The average bpm of groups A and B combined in each solution are also shown below as a percentage of the base rate. Average Number of bpm Average % of BR DMEM (Base Rate) 43 100.0 0.1 mg/ml Caffeine 52 123.3 0.2 mg/ml Caffeine 66 114.3 0.3 mg/ml Caffeine 60 105.8 0.5 mg/ml Caffeine 19 59.4 1.0 mg/ml Caffeine 0 0   Figure 11. The relationship between the caffeine concentration and the heart rate as a percentage of the base rate. The mark at zero caffeine represents the base rate in the DEM control.       One possible reason for a decrease and eventual cessation of the heart rate in the high dosages of caffeine could be an imbalance in the concentration of calcium and potassium. The high dosages of caffeine may somehow have caused an excess of potassium ions, which caused a decrease in the heartbeat and eventually death.       In the future, it would be advisable to be more precise as to how much time each heart stays in each solution and the temperature of each solution. The order in which the embryos are added to the various caffeine solutions may affect the number of beats per minute. Because DMEM contains glucose (a valuable source of energy not offered by Howard Ringers solution), each heart should be placed in DMEM for the same amount of time before entering the caffeine solutions. This study was done in two groups in which hearts where added to caffeine solutions 0.1 mg/ml, 0.2 mg/ml and 0.3 mg/ml or 0.1 mg/ml, 0.5 mg/ml and 1.0 mg/ml successively. Because the embryo cannot degrade caffeine, it is possible that the effects on the hearts measured in association with the later caffeine solutions may in fact be a result of much higher concentrations of caffeine. Future studies with the ability to use larger sample sizes might consider adding each embryo only to the two controls and one solution of caffeine rather than all the caffeine solutions in succession.
		Literature Cited Bellains, Ruth. Osmond, Mark. 1998. The Atlas of Chick Development. San Diego: Academic Press. pp. 25-29. Braun, Stephen. 1996. Buzz: The Science and Lore of Alcohol and Caffeine. New York: Oxford University Press. pp 155-156. Gilbert, Scott F., 2003. Developmental Biology, 7th ed. Sinauer Associates Inc. Publishers. Sunderland, Mass. pp. 492-8. Gwinn, Robert P. 1992. The New Encyclopedia Britannica. New York: Encyclopedia Britannica, Inc. pp. 384-390 Nishikawa, T. et al. 1985."Potentiating Effects of Caffeine on the Cardiovascular Teratogenicity of Ephedrine In Chick Embryos." Toxicology Letters. 29: (1985) 65-68. Spiller, Gene A. 1998. Caffeine. New York: CRC Press. pp. 228-229.