4 variety of saline formulae have been used with insect tissues. This iiiight be expected in view of the variety of insect habitats and diets, but the coinposition of the saline used with tissues of the cockroacli, Pel-iplmeta awwricaizn, dififers greatly in different laboratories. The extremes a r e represented by the saline used by Yeager ( '39) with the heart (Ya('1 10.93 gin, KC1 1.57 gin, CaC1, 0.55 g m , MgC1, 0.17 gm per liter), arid that used by Pringle ('38) with nerve iiruscle preparations (Nap1 9.0 gm, KCl 0.2 gm, CaCl, 0.2 gm, dextrose 4.0 p i per liter). The sodium potassium ratio in the first case is 7, in the second case 45, a variation which would certainly not be tolerated by irritable tissues in vertebrates.
Presumahly these formulae were empiricallF determined, hut a recent paper by Tohias ('47) provides accurate aiialpses of the cation content by heniolyniph, and other. tissues of tlie cockroach. His figure f o r normal potassium in roach urn is 17 milliiiioles (1.27 gm RCl) per liter, while no figures foi. calcium are giveii. Thus, tlie formula of Tcaqei. con t a ins soin e d i a t more pot as sium, w2i il e that of P r iugle
The woik descrih?d in thi.; paper was suiqorted in pait by a grant from the Permanent Scienco Fund of the American Academy of Arts and Sciences, and in part bp a contiact between the Moilical l)ivision, Chelnieal Corps, U. S. Army, arid Tufts College. T7nder the terms of this contract thr C'iinnirxl Corpq w i t h e r rrfitiicts nor is responsible for the roiirlusions of the aiitiioi.