STUDIES ON THE ACTION OF PHENYLTHIOUREA ON THE RESPIRATORY METABOLISM AND SPINNING BEHAVIOUR OF THE CYNTHIA SILKWORM

¹ Department of Zoology, University of Edinburgh, Scotland, U. K.

1. A symptom of the metamorphosis of Cynthia is that the precipitous fall in the rate of oxygen consumption begins two and a half days before the spinning period.

2. The rate of oxygen consumption is reduced to half the maximal rate of 1400 mm.³ O₂/gm. pupal wt./hr. when spinning begins. It continues to fall throughout the spinning phase and reaches a level of 75 mm.³ O₂/hr. in the early pupal stage.

3. Phenylthiourea has a pronounced depressant action on the rate of oxygen consumption, the depression being proportional to the amount of this compound introduced into the blood.

4. The decrease in respiration brought about by phenylthiourea coincides with the inhibition of blood phenolase activity. Possible sites of the depressant action of phenylthiourea on respiration are discussed.

5. When the rate of oxygen consumption is depressed to various levels at the beginning of spinning a series of qualitatively different cocoons is produced.

6. It is concluded that the pattern of spinning behaviour is delicately tuned to the metabolic rate.