788 REPORT— 1902. 



molecules are linked together. This hecomes decomposed, liberating six molecules 

 of water and six molecules of oxygen, and forming^ a hexavalent phenol whicb 

 subsequently undergoes a molecular rearrangement and becomes glucose. 



Yet another suggestion was made by Bach in 1893. He points out that when 

 sulphurous acid is exposed to light it becomes transformed to sulphuric acid, 

 sulphur and water being split ofi', and he argues that a process analogous with 

 this may take place in a leaf. The carbon dioxide uniting with water would form 

 carbonic acid, and this might then split up in the same way as the sulphurous 

 acid. The carbon and the water thus split off are on this hypothesis not set free 

 separately, but in combination as formaldehyde. The higher carbon acid, to which 

 Bach ascribes the formula HoCO^, splits up into carbon dioxide and hydrogen 

 peroxide, and the latter is decomposed into water and free oxygen. 



Lieben has still more recently put forward the view that formic acid and not 

 formaldehyde is formed by the first decompositions. He has found that leaves of 

 grasses and various trees yield formic acid among other products when mixed with 

 their own weight of water containing a trace of sulphuric acid, and distilled with 

 steam. Moreover, when carbon dioxide is acted upon by nascent hydrogen the 

 only product is formic acid. 



These speculations afford many points which might be well made the starting- 

 places of research. The views of Baeyer have met with most acceptance, though 

 but little success has attended the few efforts that have been made to establish 

 them by experiment. 



They involve several definite stages of action, of which the most important 

 seem the production of carbon monoxide and hydrogen, the formation of form- 

 aldehyde, and the construction of a sugar. The last two questions arise also in 

 connection with the hypothesis of Bach. 



If we examine the work that has been published bearing on the probability of 

 the formation of carbon monoxide in the plant we find little that is satisfactory. 

 The statements that have been made are opposed to the idea that carbon monoxide 

 is of value in nutrition ; it is said that when supplied to a plant instead of carbon 

 dioxide it does not lead to the formation of carbohydrates. It is further advanced 

 that this gas is of a very deleterious nature, and if formed would result in the 

 speedy death of the protoplasm of the cell in which it originates. This idea is, of 

 course, specious ; but it does not appear to be well founded. The deadly character 

 of carlaon monoxide when inhaled by a human being depends upon a peculiar 

 interference which it causes with the oxygen-carrying power of the red blood 

 corpuscles. The pigment haemoglobin to which these little bodies owe their use- 

 fulness forms a loose chemical combination with oxygen, the compound being 

 formed in the blood vessels of the lungs and being decomposed with the liberation 

 of the oxygen in those of the tissues of the body. It is evident, therefore, that the 

 value of the corpuscles as oxygen- carriers depends iipon their haemoglobin. When 

 this pigment is exposed to carbon monoxide it combines with it in the same way as 

 it does with oxygen, forming, however, a more stable compound. The affinity for 

 this gas which the pigment manifests is very considerable. Hence the poisonous 

 nature of carbon monoxide. It is easily seen that the latter is a poison because it 

 throws out of gear and temporarily paralyses a most essential part of the mechanism 

 of respiration, effectually preventing oxygen from reaching the tissues of the body. 

 There is no evidence here that it exerts even a deleterious influence upon the living- 

 substance itself. The only poisonous effect it would be able to exert on the plant 

 would necessarily be of the latter character, for there is no oxygen-carrying 

 mechanism that could be interfered with. We cannot lay any stress, therefore, on 

 the objection to Baeyer's view, based upon the action of carbon monoxide upon 

 the human organism. 



Another possibility may, however, be mentioned. As we shall see later, there 

 are certain resemblances between haemoglobin and chlorophyll, the vegetable 

 pigment concerned in photosynthesis. May not carbon monoxide enter into some 

 relationship with the latter, and thereby indirectly hinder its activity ? Of that, 

 however, there is no reliable evidence, the facts known to us rather pointing in the 

 opposite direction. 



