DISCUSSION 
a very much larger population than we have in the world today. 
But I think it is going to be extremely difficult to get agricul- 
turalists to increase their production of protein at a rate even 
commensurate with the present extrapolated rate of world 
population increase. The limiting factor is undoubtedly pro- 
tein and this means, in effect, a small group of essential amino 
acids which the body cannot form for itself, but which it must 
get in its diet. These include lysine and trytophan, but there 
are, of course, others. 
Clark: Lysine can be synthesized. 
Brock: There are a few amino acids which can at present 
be synthesized economically but lysine is the only one for which 
this can be done at anything like a realistic figure; indeed 
most people feel that even the figure for lysine is still completely 
unrealistic in relation to world needs. The vitamins, the 
minerals, and the trace elements are not going to present any 
problem because we will be able to synthesize them all, but 
I think some macro-elements, particularly calcium, are going 
to be very difficult to supply through vegetable diets. The 
amount of mineral fertilizers which will have to be put into 
the leached-out soils of the tropics in order to raise productivity 
is fantastic. I am talking outside my field here, but that is how 
I understand the position. 
Lederberg: Which are the amino acids which are most criti- 
cal for supplementing vegetable protein ? 
Brock: Lysine and tryptophan are among the most critical 
but it varies from vegetable protein to vegetable protein—in 
maize particularly lysine and tryptophan. 
Lederberg: Can you tell us the cost of producing synthetic 
amino acids? 
Brock: I do not recall the actual cost; it is quite cheap as 
amino acids go, but very expensive as nutrients go. 
Pirie: Like everyone else who has spoken, I cannot agree 
with Colin Clark’s first thesis, namely that the world food 
shortage is really a figment of Boyd Orr’s imagination, but I 
think that he is right in his contention that very much more 
food could be made than is in fact produced. What people 
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