In most of the experiments in animals, the analytical data followed over a certain length of time show variations which cannot be explained by the experiment itself. A direct relationship of such variations to changes occurring in the environment could be seen in the following experiment.

Six groups of 20 female white Wistar rats each, were injected on the same days, each group with a different agent. One group of animals received neutral oil as control while the others received different fatty acid preparations. The urinary surface tension was measured daily at approximately the same time of day for all the animals. The average value of these daily data was obtained for each group and used to trace the respective curves.

By comparing these curves, two characters were recognized. One was seen to concern differences from one curve to another, and consequently, would be considered as resulting from differences in the direct effect of the medications used. The other group of changes concerning variations from one day to the other, was seen to exist in all the curves, the curves having thus parallel variations. (Fig. 262) These variations, common to all the curves, were considered induced by a general influence. The analysis of these curves shows that the first kind of changes, related to the agents used, concerns differences in the levels of the curves themselves, when compared with that of the control. Treatment with stearic acid does not influence the level, and treatment with oleic acid has only a slight influence. A manifest change is seen for the other curves. The urinary surface values correspond to lowest values for linoleic acid (d) and for cod liver oil fatty acid (e). Some less marked differences from the control curve is seen for the fatty acid preparation obtained from cow spleen (f).

Independent of these level differences, all the curves of the controls as well as of the treated groups show parallel daily changes. An exception is seen for the curve for oleic acid, which shows opposite variations. We do not have an explanation for this discrepancy. The parallel change would indicate the intervention of a common factor, independent of the experiment itself. By relating these changes to those taking place in the environment, the common variations in the curves could be recognized to follow— in an opposite sense—those of the environmental temperature.

Curves of the average value of the urinary surface tension in groups of rats

Fig. 262. Curves of the average value of the urinary surface tension in groups of rats treated with different fatty acid preparations (1 cc of 10% in oil daily). The parallel changes in the curves, except for oleic acid when the variations are opposite—indicate a common external influence. The differences in the relationship of the curves to the average value line, corresponds to the direct influence exerted by the agents.

It should also be noted that this environmental influence is progressively more accentuated for the curves where the level of the surface tension is lowered as a result of the agent administered. This correlation would suggest the possibility that the action exerted by the environment would take place largely through changes in the intervention of the fatty acids of the organisms themselves.