SECTION M.—AGRICULTURE. 279 
During the growth of the crop advisory work is largely restricted to 
the domain of diseases and insect pests, whose ravages take incalculable 
toll of our crops. ‘This section of advisory work | am not competent 
to discuss, but I am continually impressed by its importance as I note 
how largely such matters bulk in the inquiries for assistance which 
pass through my hands, and I believe science can make no more directly 
effective contribution towards the removal of at least the technical 
difficulties of the farmer than the elaboration of effective preventive 
measures against pests and diseases. 
In some directions, as in the circumvention of certain diseases of 
potatoes and cereals, very striking advances have already been made, 
to the great benefit of practice ; but in all too many cases the adviser at 
present can go little beyond the stage of diagnosis, although, with the 
greatly increased number of research workers now available, there are 
good grounds to hope that the lines of preventive action may before long 
be worked out. 
I must pass on, finally, to the utilisation of crop products as food for 
animals, the line of work with which my own personal interests and 
activities have always been most closely associated. Looking back over 
twenty years of advisory activity, I realise that the position of the 
adviser in animal nutrition is infinitely stronger to-day than when I 
first assumed the réle. 
At the outset of this period the feeding of animals was regarded 
simply as a matter of supply of suitable proportions of digestible protein, 
oils, and carbohydrates, more or Jess regardless of the character of the 
materials in which they were supplied. Little further could be done in 
the way of differentiating the values of different food materials beyond 
a comparison upon the basis of gross digestible energy, although the 
conclusions to which this led were notoriously unreliable and in many 
cases in flagrant conflict with practical experience. Material for a 
great advance was, however, rapidly accumulating in the work of 
Kellner, which was finally reduced by him to a practical system of food 
evaluation in his classic ‘ Ernibrung der landwirtschaftiichen Nutztiere,’ 
published in 1905, and universally acclaimed as representing a great 
advance in the application of nutritional science to the practical feeding 
of farm live-stock. The advance lay essentially in the discrimination 
between the available energy and the net energy of foods, and the 
carrying out of a sufficiently large number of determinations of the latter 
to furnish a fairly adequate basis for generalisation. With these to 
supplement his classic determinations of the values of protein, fat, and 
carbohydrate for the production of fattening increase, he was able to 
devise a practical scheme of assessing the production-values or net 
energy-values of foods, which he preferred for reasons of practical con- 
venience to express in terms of starch. The significance of the great 
practical advance made by Kellner was not at first clearly grasped in 
this country, critical attention being directed, in accordance with true 
British conservatism, more to the admitted shortcomings of the starch- 
equivalent than to its merits; but as time revealed its superiority over 
the older methods it came generally into use, and now serves as the 
basis of all our advisory work in farm nutrition. 
