MATERIALS AND METHODS

In the first group of experiments, the technique used by Weed (1914a) and Patek (1944) was repeated in as much as the intravenous administration of hypertonic saline was employed in an attempt to facilitate the passage of indian ink injected into the subarachnoid space of an adult rat into the perivascular channels, thus rendering these channels easily identifiable in histological sections. As a result of the experience gained in this first group of experiments, a new technique was evolved which differed from those previously employed in the following particulars:(1) The new-born rat was used as the experimental animal.(2) The indicator was injected into the subarachnoid space in very small quantities (0.05 ml.) daily for periods of up to 3 weeks.(3) The indicator chosen was' dag'colloidal carbon (Acheson Colloids Ltd.) in which 99% of the particles were less than 1, t in diameter.(4) Intravenous hypertonic saline was not administered. The experimental details in the two groups were as follows.