6 METABOLISM IN THE NORMAL FUNCTIONAL STATE 



as the cat or dog, the skull must be opened under anaesthesia and 

 liquid nitrogen or oxygen then poured on to the exposed cortex. 

 Such a technique necessarily introduces the added complication of 

 the effects of the anaesthetic in addition to those being studied. 

 A fuller account and details of techniques are given in the Appendix. 

 The values given in Table 1 were all obtained by this method with 

 the exception of those from the rats studied by Abood et al. (1952) 

 and Koransky (1958). In these experiments the animals were first 

 decapitated and the brain rapidly removed and frozen in solid 

 carbon dioxide or a mixture of carbon dioxide and acetone, before 

 extracting the acid soluble phosphates. 



The list given in Table 1 represents an accumulation of data 

 over several years by many different investigators using different 

 analytical methods, ranging from simple salt precipitations to 

 chromatographic and enzymic techniques. Many of the results 

 were obtained incidentally to other investigations and must perhaps 

 be regarded with some reservations. Taken as a whole, however, 

 with the exception of the monkey, the quantities of phospho- 

 creatine show a marked similarity in all species, averaging some 

 3-0 /xmoles/g wet wt. tissue. Values for the quantities of inorganic 

 phosphate show a similar agreement being about 4-0 /xmoles 

 phosphorus/g wet wt. On the other hand quantities of adenosine 

 polyphosphates show considerable fluctuation, adenosine triphos- 

 phate ranging from 0- 62-4*4 /xmoles/g wet wt. and adenosine 

 diphosphate from 0-2-38 /xmoles/g wet wt. These differences are 

 probably attributable to the analytical methods employed, details 

 of which and possible sources of error are given later (Appendix). 

 Probably the results of Kratzing and Narayanaswami (1953) and 

 Thorn et al. (1955), who used specific enzymic methods, are the 

 most accurate of those listed. Certainly high levels of adenosine 

 diphosphate are not compatible with a system actively carrying 

 out a vigorous oxidative phosphorylation. With these considera- 

 tions in mind, 2-5-3-0 jitmoles adenosine triphosphate/g wet wt. 

 tissue would appear to be a reasonable normal level. 



Other nucleotides present are found in much smaller amounts 

 and quantitative data are still very scanty (Table 2). Of them, 

 guanosine nucleotides constitute by far the greatest quantity. 

 It is of interest that the presence of such nucleotides was first 

 postulated by Kerr (1942), who found that 17-3% of the total 

 nucleotide nitrogen of dog brain was in the form of a purine 



