i62 THE CARBOHYDRATES 



be expected that during light, provided always the other re- 

 quisite conditions obtained, the hexoses would increase in 

 amount. So far, this has not been satisfactorily proven. It is 

 to be borne in mind, however, that a portion of these hexoses, 

 in all probability, would be used for the immediate require- 

 ments of the plant : thus a certain proportion would be im- 

 mediately used up in respiration ; another part might possibly 

 be accounted for as being necessary for the synthesis of pro- 

 teins ; again, a certain quantity would be translocated to other 

 parts of the plant ; finally, it must not be forgotten that the 

 whole process of photosynthesis takes place with extraordinary 

 rapidity, starch, a final product, often appearing directly after 

 the chloroplast is exposed to light. 



Considering first the formation of a simple sugar, it is 

 possible, of course, that the formaldehyde may at once under- 

 go polymerization into a polyose sugar ; but this can only 

 be assumed when all intermediate products have been proved 

 to be absent. And, as regards these intermediate products, 

 although our present physiological knowledge is decidedly 

 scanty, indeed, practically non-existent, there are certain lab- 

 oratory facts which are of the greatest importance. 



As already mentioned above, the molecular formula of a 

 hexose shows that it is a polymer of formaldehyde. The first 

 successful attempt to bring about such a polymerization was 

 made by Butlerow in 1861, who, by the catalytic action of 

 lime water, at the ordinary temperatures, on trioxymethylene 

 (itself a polymer of formaldehyde), obtained a syrup with a 

 somewhat bitter taste, which he called methylenitan. Sub- 

 sequently Loew undertook an investigation of the action of 

 milk of lime on formaldehyde, and devised the following ex- 

 periment. A four per cent solution of formaldehyde is mixed 

 with an excess of milk of lime and repeatedly shaken for about 

 half an hour ; after filtering, the mixture is set aside for some 

 days until the pungent smell of formaldehyde has disappeared. 

 The solution, which will now reduce Fehling's solution, yields 

 a colourless syrup with a very sweet taste. This substance, 

 which is known as crude formose, was examined by Emil 

 Fischer, who found it to consist of a mixture of various hex- 

 oses and succeeded in isolating from it a small quantity of a 

 sugar — acrose. This same sugar can also be obtained by the 



