258 SECTIONAL ADDRESSES 
residues in a chain through positions 1 and 4 of the glucose molecule is 
the fundamental principle of modern cellulose structure. By purely 
chemical methods of investigation, they have shown that in some forms 
the cellulose is a straight chain of limited length containing not more than 
100 cellobiose or 200 glucose units. 
The question of the size of the cellulose molecule has been attacked 
by various other methods—by viscosity measurements of cellulose dis- 
solved in Schweizer’s reagent or of the acetate or nitrate in organic media 
(Staudinger), by study of the cleavage products obtained by enzymes and 
by the X-ray methods of the Braggs and of Mark. The interesting fact 
emerges that the results obtained by the X-ray investigations of cellulose 
structure are in such wonderful agreement with the views adopted from 
chemical methods. Sir William Bragg pointed out in a lecture recently 
delivered to the Royal Institution that cellulose is the fundamental mole- 
cular combination occurring in vegetable growth and that it is pre- 
eminently the molecule of growth in the vegetable world. The cellulose 
occurring in plants cannot have the same properties in all directions for 
growth takes place along definite lines. The fibrous nature of cellulose 
has long been recognised, as we see by the use which is made of it in 
spinning threads and ropes which can stand an immense strain in one 
direction. Bragg’s investigations have shown that cellulose is made up 
of crystals, or crystallites, invisible under the microscope, but capable of 
detection by X-ray methods. These crystallites are partly oriented, 
having one direction more or less in common and to this arrangement of 
the crystallites the peculiar and characteristic properties of cellulose are 
due. Recent studies by Thiessen have indicated that the structure of 
the pure cellulose fibre is the same as that of lignified tissue, except that 
the spacing in the latter is wider to accommodate the lignin. Reference 
has already been made to the fact that the organic matter of the soil is 
derived from this lignin complex from which the cellulose has been 
removed. 
It has already been noted that the various stages in the building up of 
carbohydrates in plants have not yet been satisfactorily explained. At 
the same time, much work of the highest importance on the composition 
of the chlorophyll in plants, the active agent in the utilisation of the 
radiant energy from the sun, has been accomplished during the last 
twenty years. In 1912 Willstétter and his co-workers at Munich 
showed that chlorophyll as ordinarily obtained is really a mixture of 
two substances, chlorophyll a (C;;H,,O;N,Mg) and _ chlorophyll 6 
(C;5;HyO,N.sMg). They also investigated the yellow or reddish-brown 
pigments, carotene (C4yyH;,) and zanthophyll (Cy9H;,02), which accom- 
pany the chlorophylls and which are generally referred to as the carotinoids. 
By a series of brilliantly conceived investigations, Willstatter has been able 
to throw much light on the structure of these complicated bodies and, 
in particular, on the relation between the chlorophyll of plants and the 
hemoglobin of blood. In this connection reference must be made to 
the work of Hans Fischer who has already synthesised hamin and made 
great advances towards the synthesis of chlorophyll. 
Enzyme Action.—It has long been known that enzyme action plays a 
