M.—AGRICULTURE 259 
highly important part in most of the chemical reactions taking place in 
plants and animals. In addition, the breaking down of complex mole- 
cules by the action of enzymes is often employed in investigating the 
constitution of these substances. 
The action of enzymes has been known for over 100 years. Kirchhoff 
in 1814 had discovered the catalytic action of the glutinous component 
of wheat meal, and later, in 1833, Payen and Persoz separated an active 
preparation of this enzyme from malt, the enzyme now known as amylase. 
While much work of a preliminary kind was carried out in the succeeding 
years, the results obtained were frequently inconsistent and confusing. 
This is not to be wondered at when we consider the excessive complexity of 
these bodies, the difficulties of purifying them and the extremely com- 
plicated reactions in which they play a part. It is again Willstitter, 
whose brilliant work on chlorophyll has just been described, who has been 
mainly responsible for the great advances which have been made in our 
knowledge of the enzymes during the past fifteen years. He began by 
improving the technique of the methods of preparation, introducing 
quantitative methods of control, and in this way was able to prepare 
specifically pure enzymes. ‘This has led to a much more accurate know- 
ledge of the specification of enzymes and has cleared up much of the con- 
fusion which existed previous to his work. He has investigated the 
colloidal characteristics of enzymes, the significance of the H-ion concen- 
tration of the medium and the action of enzymes as synthetic agents—to 
mention only a few of the outstanding results.. In addition, a rational 
classification of the enzymes is now possible and much more detailed 
information about their specific action is available. While the chemical 
constitution of the enzymes has not yet been solved, there is no doubt that 
the results of Willstatter and his school have been most stimulating to 
those engaged in bio-chemical research and have had an important appli- 
cation to the many industries which make use of enzymes in manufacturing 
processes, 
Vitamins—A discovery which will always be associated with the 
name of the distinguished President of the Association this year 
(Sir Frederick Gowland Hopkins) is the importance in nutrition of the 
accessory food substances now known as vitamins. As far back as 1881, 
it was noticed that milk cannot be replaced by an artificial mixture of its 
chief constituents. In 1905 Pekelharing of the University of Utrecht 
made the striking claim that there is an unknown but essential substance 
in milk and other foods which is essential to nutrition. This work was 
overlooked, and it was not until the publication of Hopkins’ work in 1912 
that general interest was attracted to the subject. The progress since 
then in the study of these bodies is most striking. One of the most 
remarkable facts which have resulted from these investigations is the large 
number of substances of the vitamin type required for the proper nutrition 
of the higher animals, the number being stated to be at least nine. Ordi- 
narily, five different vitamins are recognised, designated A, B, C, D and E. 
Vitamin B is now subdivided into no less than five substances, commonly 
referred to as the Vitamin B complex. 
Vitamin A,—It is now fairly definitely established that Vitamin A is 
