256 SECTIONAL ADDRESSES 
the theory of substitution and types and the theory of structure. These 
investigations gave a great impetus to organic synthesis and the number of 
known carbon compounds increased rapidly. Most of the substances 
investigated, e.g. the many products obtained from coal tar, had no 
connection with animal or plant life, and organic chemistry became much 
more the chemistry of the carbon compounds than that of living organisms. 
Until the beginning of the present century, the interest in the chemistry 
of natural products steadily declined, and it is only since then that the 
development of Bio-chemistry, as we know it now, may be said to have 
taken place. The monumental work of Emil Fischer on the purines, the 
simpler carbohydrates, the proteins and the tannins, to which he devoted 
the greater part of his life, laid the foundations of this new branch of the — 
science. His method for the separation of the amino-acids by first con- 
verting them into esters and then separating the esters by fractional 
distillation under greatly reduced pressure, has been invaluable in thé 
study of this group of substances. By 1906 bio-chemistry as a separate 
branch of the science may be said to be firmly established, and in that year 
three journals devoted entirely to bio-chemistry appeared in Britain, the 
United States and in Germany respectively. ‘The work initiated by 
Fischer has been carried on by a brilliant band of workers in this and 
other countries, amongst whom may be mentioned Perkin, Willstatter, 
Gowland Hopkins, Robinson, Barger, Haworth, Windaus, Wieland, 
Hans Fischer and Dakin. 
It is obvious that the investigation of the chemical changes which take 
place in a living cell presents difficulties of a very high order. The 
reactions involved take place in very dilute solution ; the intermediate 
bodies formed have a very brief existence, being rapidly changed into 
some further product ; so that, while we may know the initial substances 
involved and the final product of the reaction, there may be little known 
as to the various stages in the formation of the final product. 
While there have been great advances in our knowledge of the structure 
of many of the substances found in plants and animals, we still know rela- 
tively little about the processes by which they are formed. ‘The various 
stages in the fundamental process of photo-synthesis have not yet been 
worked out, although plausible suggestions as to what takes place have not 
been wanting. We are ignorant of the stages by which amino-acids in 
plants are formed from nitrates and carbohydrates and little is known of 
the methods by which carbohydrates are changed into fats and vice versa. 
In the same way, while we have a considerable amount of knowledge as 
to how the proteins, fat and carbohydrates are broken down in animals, 
little information is as yet available as to how similar changes are brought 
about in plants. A notable recent advance is Robinson’s theory of the 
way in which alkaloids are synthesised in plants, which has enabled him 
not only to predict the constitution of certain alkaloids, but also to effect 
the synthesis in vitro of alkaloids and alkaloid-like substances. 
It is interesting to note in passing that where individual instances of 
katabolism have been worked out, the breakdown does not occur, as a 
rule, in the manner which the organic chemist would expect. The same 
is true of the degradation of the amino-acids in the animal body. 
