The turbidimetric estimation of hyaluronidase.

2. Tests with known mixtures of phosphate esters and the recovery of the phosphorus of muscle extracts from the chromatograms suggest that the individual values obtained with the method in its present form are reliable to within 10 %. 3. Trichloroacetic acid extracts of muscle have been found to contain certain phosphate esters not yet identified. 4. The pyrophosphate fraction present in the extracts is found to be entirely in the form of adenosine triphosphate and adenosine diphosphate. 5. Striated muscle from tortoise, which is about ten times slower than that from frog, contains less adenosine triphosphate and creatine phosphate + orthophosphate than the latter. 6. The chromatographic method has been used to repeat some of the classical experiments on the metabolism of intact muscle and the results of these experiments have been confirmned. 7. An attempt has been made to follow the changes in tortoise muscle during the early stages of activity. The most prominent ones are a decrease in the 'high-energy' phosphate (two-thirds adenosine triphosphate + one-half adenosine diphosphate + creatine phosphate), largely in the creatine phosphate component, and an increase in the monophosphate ester fraction. I should like to thank Dr E. J. Harris for his constant interest and advice. Part of the expenses for this work were defrayed by the Medical Research Council.