THE PROBLEM AND METHODS OF INVESTIGATION 73 



the organism which are associated with metabolic activity. Thus 

 the metabolic condition of different individuals or parts may also be 

 compared by means of this indirect or acclimation method. 



These differences in susceptibility to narcotics, particularly 

 those determined directly with relatively high concentrations, 

 afford, when properly controlled, a very delicate method for com- 

 paring general metabolic rates in different individuals and parts, 

 at least in many of the lower animals. In a recent paper (Child, 

 '130) the technique of the method for flatworms and similar forms, 

 its different modifications and its limitations have been considered 

 at length. As regards the relation between susceptibility or resist- 

 ance to cyanide and rate of metabolism, it was shown in that 

 paper that susceptibility is altered by motor activity, that the 

 temperature coefficient of susceptibility is of the same order of 

 magnitude as that of most chemical reactions, and that differences 

 in carbon-dioxide production correspond to differences in suscepti- 

 bility. 



The estimations of carbon-dioxide production were made by Dr. 

 S. Tashiro with the "biometer" devised and recently described by 

 him (Tashiro, '136). The sensitiveness and great value of this 

 apparatus are shown by the fact that Tashiro has been able to 

 demonstrate the production of carbon dioxide in the resting nerve, 

 its increase by stimulation, and its decrease by narcotics, and has 

 also shown that living seeds resemble the nerve in most respects as 

 regards irritability (Tashiro, J i$a). In the comparison between the 

 results of the susceptibility method and the carbon-dioxide produc- 

 tion the flatworm Planaria dorotocephala (see Fig. 6, p. 93) was 

 used in most cases. The susceptibility method shows that the rate 

 of metabolism is higher in young than in old animals, in starved 

 than in fed, and in animals stimulated to movement than in resting 

 animals. In distilled water the rate of metabolism as measured by 

 the susceptibility method is higher and in 5 per cent sea-water lower 

 than in tap-water. In pieces isolated by cutting, the rate of metab- 

 olism is higher in long anterior pieces than in posterior pieces of 

 the same length (cf. Child, '146). In each of these cases the animal 

 or piece which possessed the higher rate of metabolism according 

 to the susceptibility method produced more carbon dioxide than 



