That disease might be due to lack of some essential factor in the diet had little place in

the thinking of 50 years age. . (46) As deficiency diseases came to be recognized and understood, the next step was the realization that lack of nutritional and endocrine factors affects primarily the chemistry of the body. Disease resulting from a "biochemical lesion' and structural changes are late effects, secondary to change in function.

This revolution in medical thought had profound consequences. The great nutrition- al diseases that flourished within the lifetime of some doctors still in practice have now vanished wherever medical knowledge has been linked with proper administration of food supplies. (47) Yet in the streets of our big cities we still see elderly people, bandy-legged, stunted and pigeon-chested, who carry the scars of it. Pellagra, prior to 1940, affected tens of thousands of poor people in the southern states of the USA; better knowledge of nutritional needs and, above all, improved economic circumstances have largely swept it away. The classic nutritional diseases occur only in situations where there is a failure both of food supplies and medical care that regrettably is still the case in many parts of the world.

Even in times of severe food shortage, proper application of medical knowledge can do much to overcome the worst effects of qualitative dietary deficiencies; medicine can deal with beriberi, scurvy and pellagra, but has no direct means of treating the effects of underfeeding—under-nutrition. (48)

The present world population is estimated to be more than 3,500 million and in- creasing by 70 million per year. In the absence of major catastrophes, there will be more than twice as many inhabitants in the world by the year 2000 as there are today. (49) The greatest threat to the well-being of mankind is this explosive population growth rate. One third of the world' s population receivers less than 2,000 kcal/ head/day. Agricultural production is hampered by had climates, soil erosion, lack of fertilizers, antiquated farming methods, political upheavals and war. This situation will steadily deteriorate unless national programs of population control and family planning based on modern contraceptive techniques are evolved and effectively put into operation. (50)

A. Consequently, lack of sufficient food continues to be a most serious cause of bad health in many underdeveloped regions.

B. Florid rickets is now a clinical curiosity in Britain.

C. Pathology is the study of disease by scientific methods.

D. This is not due to an increase in human fertility but is caused almost entirely by a remarkable reduction in the death rate.

E. Consequently, the concept of deficiency diseases, nutritional and endocrine, grew in the present century.

F. In addition, food production must be greatly in creased by the use of high-yielding strains.

(46)