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Mr. F. Kidd. 



From the foregoing Table, then, it appears that, when oxygen is not present 

 in excess but in deficiency, a rise in the percentage of carbon dioxide in the 

 atmosphere produces no corresponding fall in the oxygen consumption. This 

 is in direct contrast to the descending series of figures representing the oxygen 

 consumption when oxygen was present in excess. 



This result strongly supports the first of the two hypotheses which have 

 been put forward above. For, as the above results show, we can reduce the 

 amount of available oxygen normally present in excess till a point is reached 

 beyond which the rate of the first or splitting process producing oxidisable 

 substances is no longer the factor limiting oxidation, but oxygen itself becomes 

 instead the limiting factor ; and in this case carbon dioxide has no longer any 

 effect in reducing the amount of oxidation. 



In short, the results thus obtained appear to offer considerable support to 

 the general theory as to the genetic relation between anaerobic and aerobic 

 respiration set out in full above. 



Section VII.- — Carhon Dioxide Narcosis. 



In these researches, we have been concerned with the narcosis due to 

 carbon dioxide which becomes apparent by retardation and inhibition of 

 growth. The universal presence of CO2 in living tissues makes it important 

 to know the details of its action. At present it is, perhaps, best to consider 

 the effects of CO2 apart and not as the basis for generalisations as to the 

 nature of narcosis. We have obtained, so far, the definite result that carbon 

 dioxide reduces both the amount of anaerobic respiration and the amount of 

 aerobic or normal respiration to a marked degree in plant tissues. Further, 

 that of the two types of respiration included under these heads, demonstrated 

 by Blackman and others, namely, floating respiration and protoplasmic 

 respiration, it is the former only which is depressed, and that this may be 

 retarded to practical inhibition under the action of C0 2 . 



It seems of importance to determine in the sequel what effect the membranes 

 of cells of various types and various tissues may have upon the tensions of 

 oxygen and carbon dioxide actually within the cytoplasm, effects for instance, 

 such as are indicated in Loeb's experiments upon artificial fertilisation in 

 which the destruction of a cortical layer in the cell was found to increase 

 largely the rate of oxidation. R. Lillie has put forward the hypothesis that 

 the cortical layer of the unfertilised egg prevents the diffusion of CO2 from 

 the egg and that this CO2 inhibits oxidation. Further, it must be determined 

 what effects oxygen and carbon dioxide themselves may have in changing the 

 general permeability of cell membranes, such as, for instance, are indicated in 

 researches like those of Osterhout and Lepeschkin in plant tissues, and those 



