Received from the Meakins-Christie Laboratories and Department of Physiology, McGill University, 3775 University St, Montreal, Quebec H3A 2B4, Canada.

Reprint requests to Dr. Milic-Emili.

^*Fifteenth Annual Becton-Dickinson and Company and Oscar Schwidetzky Memorial Lecture.

Accepted for publication July 9, 1960.