12 CHEMICAL MANUKES. 



they exhibit in plants in general. A deeper study of these products 

 shows us the point at which it is impossible to make clear and exact 

 distinctions between them. 



We have placed the cellulose (so called because it forms the warp 

 of vegetable tissue) at the head of the first group ; immediately after 

 comes the starch or amidon, then the gums, and lastly the sugars. 



Between the cellulose and the sugar there are great and numerous 

 differences, and if one did not know the other terms of the series 

 pectin, inulin, gums, etc. it would not occur to one to see in these 

 two bodies dissimilar forms of an unique type. 



Cellulose is insoluble in water the sugar, on the contrary, melts 

 away in it. 



Cellulose is not easily attacked by acids or alkalies slightly diluted. 

 Sugar is easily changed by both. Sugar has a sweet taste, cellulose 

 no taste. 



How did we get the idea of assimilating these two bodies, so as to 

 make of them one and the same body ? 



The identity becomes manifest, and almost forces itself upon us, if 

 we do not confine our observations to the cellulose of woody tissue, 

 but look also at the properties of the other terms in the series, and at 

 the changes to which the cellulose itself is subject. 



Cellulose in the form of woody tissue is insoluble in cold water, 

 and even in boiling water. But in Iceland moss cellulose, being less 

 compact, jellies as soon as boiled. Hard as ivory in the kernels of 

 some fruit, it becomes edible in the mushroom. There is no greater 

 difference between the edible part of the mushroom and a piece of 

 the wood of an oak than between the sugar and cellulose of the 

 lichen. 



The cellulose in the tubercles of the Irish potato is in isolated 

 grains, formed by concentric layers fitting into each other. 



Between the amidon and the cellulose there is little apparent 

 analogy ; but if we add that the amidon swells in boiling water to 

 such a degree as to form a true jelly, like Iceland moss, the analogy 

 between the two products becomes incontestable. 



Amidon swells in boiling water without dissolving; but inulin, 

 which is found in the tubercles of the Jerusalem artichoke, and which 

 is a species of amidon, dissolves in boiling water, from which it sep- 

 arates itself in independent grains as the water cools. 



If we add that gum-dragon forms jelly in cold water without dis- 

 solving, and that gum-arabic swells and dissolves in it, and has a 

 slight taste of sugar, the change of the gum into sugar becomes 

 evident, and the analogy which joins the sugar to the cellulose, 

 though at first concealed, can no longer be doubted. 



To prove this conclusion, I will add, that the cellulose itself, even 

 when most compact, can be changed into gum and to sugar, and to 

 do this it is only to be treated with sulphuric acid that it is the 

 same with all the other terms of the series, which can all be turned 

 into sugar by the same means. These transformations are incessant 

 in vegetation ; the economy of vegetable nutrition depends upon them, 

 as I will show when I come to speak of albuminous substances. The 



