1. The biologic experiments with the links of the methane series—n-pentane, n-hexane, n-heptane, n-octane, i-octane, and pentene—gave these qualitative results: (a) The higher the number of CH2 groups, the longer the chain, the longer the average lifetime of the animal. (b) The ramified chain does not appear to act differently from the saturated straight chain with the same number of C atoms. (c) One double bond within the chain shortens the lifetime to a considerable degree.

2. The quantitative discussion shows that the lifetimes depend exponentially on the molecular weight.

3. Qualitatively the hypothesis is supported that with rising molecular weight the concentration of CH2 groups within the animal diminishes according to the vapor pressure or the thermodynamic potential. However, lifetime and these physical properties obey different functions.

4. These physical properties are of high biologic importance. But they are not sufficient to explain the biologic effects quantitatively.

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