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When cerebral tissues are kept in cold media they lose their normal metabolic response to applied electrical pulses (Marks & Mcllwain, 1959). Response can be restored by incubating with tissue extracts and blood-plasma fractions, and the activity of such fractions has been correlated with their content of neuraminic acid derivatives (Mcflwain, 1960 a, 1961a). The most potent of these derivatives examined were the cerebral gangliosides, and it has therefore been considered that more might be leamed about cerebral excitability by measuring the quantity of gangliosides and of related substances in the brain and in isolated cerebral tissues prepared and maintained in different fashions, including especially those kept in cold media and incubated with various additional substances. The gangliosides (for nomenclature see McIlwain, 1961c) contain fatty acids, sphingosine, N-acetylgalactosamine and glucose as well as the N-acetylneuraminic acid by which they are most frequently determined (Svennerholm, 1957; Klenk & Gielen, 1960; Rosenberg & Chargaff, 1960; van Heyningen & Miller, 1961); they comprise more than one molecular species (Meltzer, 1959; Folch & Lees, 1959; van Heyningen & Miller, 1961). Cerebral tissues also contain derivatives of N-acylneuraminic acids (sialic acids) which either are not gangliosides or are further derivatives or complexes of gangliosides (Svennerholm, 1956; Rosenberg & Chargaff, 1958; and see below), and the particular distribution of gangliosides between aqueous salt solutions and non-aqueous solvents, investigated by Folch, Lees & Sloane-Stanley (1957), gives valuable means of obtaining additional specificity in methods for their determination. Long & Staples (1959) applied such distribution in a method for separating and determining the gangliosides, which forms the basis of that studied below. We have, however, given further attention to two aspects of the determination: (1) the completeness of extraction of the lipidsoluble neuraminic acid derivatives; (2) the use of an alternative spectrophotometric method for the measurement, namely the thiobarbiturate method of Warren (1959), as well as the ferric chlorideorcinol reaction as used by Long & Staples (1959). EXPERIMENTAL

Gangliosides and related substances of isolated cerebral tissues examined in relation to tissue excitability