¹ From the William G. Kerckhoff Laboratories of the Biological Sciences, California Institute of Technology, Pasadena

An investigation has been made of the phosphate and lactic acid changes in the adductor muscle of the cheliped of the crayfish Cambarus clarkii upon stimulation of the isolated axons for the fast and slow contractions at determined frequencies. The data obtained point to the following conclusions:

1. When the mechanical effects of the two types of contraction are the same, the chemical changes are of the same order. If the mechanical effects are different, the chemical changes likewise are not equivalent. This is especially to be seen in the case of stimulation at 50 shocks per second: a slowly rising, long continued, strong slow contraction takes place with no apparent change in the phosphate content; a quickly rising fast contraction occurs with a large increase in the phosphate.

2. Since equivalent chemical changes accompany equivalent mechanical action, the two types of contraction do not differ in the essential mechanism of the chemical changes involved, and only one type of contractile substance is present.

3. Even when a contraction has taken place to the maximum extent obtainable, only enough phosphate is found to correspond to one-fifth to one-third of the available phosphagen.

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