TRANSACTIONS OF SECTION I. 7G3 



Were a complete exposition of this subject possible it would include three 

 main sections : (1) What is the nature of the chemical reaction or complex of 

 reactions that constitutes respiration ? (2) To what extent can this reaction in 

 the cell be shown to conform to the laws of general chemistry, in the matter of 

 reaction velocity, temperature-coefficients, mass of reacting substances, influence 

 of katalysts and foreign substances ? (3) What is the influence upon the progress 

 of the reaction of the peculiar medium, protoplasm, in which it takes place '! 



(1) A summary statement of respiration takes the form of the equation for 

 the complete oxidation of glucose. From this simple equation physiologists 

 have been driven to make continually more and more complicated pictures of 

 what actually happens intermediately in respiration. 



The first complication was introduced by the discovery of ' anaerobic ' respira- 

 tion and the separation of oxidation-processes from anaerobic splitting of- 

 glueose. This raises the questions : What are these splitting products ; do they 

 form the first stage of normal respiration, and are the end products of splitting 

 (such as alcohol) the bodies oxidised or are less stable precursors of alcohol 

 oxidised in presence of air ? 



The second complication arises in connection with oxidation. None of the 

 probable substances formed by splitting oxidise spontaneously to CO, and H,0. 

 Some special chemical machinery is needed to explain the oxidation. The 

 simplest chemical oxidation is now regarded as a complex phenomenon, still 

 more so oxidation in the cell. Oxidative agents are generally present, some of 

 which may be true enzymes — oxidases — and others only carriers of oxygen; but 

 there is the difficulty that aliphatic compounds are but little attacked by them, 

 and the oxidation seems never to be complete. 



Palladin's theory of respiratory chromogens maintains that these chromogens, 

 which are aromatic substances, are oxidised by oxidases and then act as carriers 

 of oxygen to the splitting products of glucose. 



(2) The physical chemistry of the respiration reaction, (a) Influence of 

 temperature, (b) Influence of concentration of the reacting substances, oxygen, 

 protoplasmic catalyst, and sugar. An account of the writer's experiments on 

 starvation and nutrition of leaves, the respiration of starchy and sweet potatoes. 

 Hypothesis that normal respiration consists of two processes, a small ' proto- 

 plasmic ' respiration, which cannot be suppressed without death, and a larger 

 ' floating ' respiration, which fluctuates with the sugar supply and can bs 

 abolished by starvation, (c) The effect of chemical ' stimuli ' upon respiration. 

 These act in several different ways which are of considerable theoretical interest. 



(3) Protoplasm may be regarded as a honeycomb structure of colloidal semi- 

 permeable septa. A medium of this nature introduces complications not found 

 in reactions in vitro. 



Alterations of internal permeability may affect the spatial separation of 

 interacting substances and so change the magnitude of respiration and other 

 processes. 



The work of Lepeschkin has shown that variations of protoplasmic permea- 

 bility, produced naturally by light and other causes, also by chloroform, etc., 

 are important factors in cellular physiology. 



The relation of respiration to the break-down of the specific organisation of 

 protoplasm, as illustrated by long-continued starvation experiments with leaves. 



(ii) The Biochemistry of Respiration. By Dr. H. M. Vernon. 



Living tissues contain oxygenases, or substances which absorb molecular 

 oxygen, bind it up to form peroxides, and so render it more active. They also 

 contain peroxidases, or activators, which greatly increase the oxidising power 

 of the oxygenases. Many, or perhaps all, the tissue constituents can be oxidised 

 by means of these ferments acting together. Thus Fenton in 1894 showed that 

 H 2 0.,, in the presence of an activator such as FeSO,,, could easily oxidise 

 tartaric acid ; and Dakin has recently shown that it can oxidise amino acids, 

 as R.CH .NH : .COOH to NH 3 + C0 2 +R .CHO. The aldehyde is then further 

 oxidised, and is ultimately converted into CO.,-f-H 2 0. All fatty acids from 

 formic to stearic can undergo this oxidation. Carbohydrates can be similarly 

 oxidised. Tissue respiration seems to be dependent on enzyme action, as it 



