290 DIETKTK" DEFICIENCY. 



studj' of nutritional problems. The pioneer work of liniil 

 Fischer upon the chemical constitution of the protein molecule 

 opened up a new field for research. His demonstration of the 

 fact that the protein molecule can be broadly rej:(arded as a com- 

 plex structure of amino-acid units led to the study, by numerous 

 investigators, of the constituent units of the different proteins of 

 plant and animal origin, which could be isolated in a stifificient 

 state of purity for detailed examination. .Linked to this came the 

 study of the physiological significance of these units. 



About the same time came a growing emphasis tipon the 

 " lipoid " portion of a diet — i.e., of those constituents, including 

 the fats, which had hitherto l)een classed amongst the fats on 

 account of their similarity in physical and solubility characters 

 and their association with chemical groupings characteristic of 

 the known fats. (irowing im])r(;vements in the technique of 

 biochemtstry have sinuxltaneously resulted in a more detailed 

 ■studv of the part ])la\ed l)y carbohydrates and minerals in the 

 animal economy. 



We are, however, in the present discussion, concerned not 

 so much with the destiny and function of the numerous chemical 

 compounds Vv'hich at the present day represent the sub-divisions 

 in the classification of the earlier physiologists, as with the condi- 

 tions arising when any essential one of them is missing. That is 

 to say, we are concerned with the i>roblem of " dietetic defi- 

 ciency." 



We need not discuss in detail the gross deficiency of all food 

 which leads to death by starvation ; nor protein-hunger, which 

 may be regarded as a form of delayed general starvation; n ;r 

 need we deal with the abnormal conditions arising on a diet of 

 pure fat where both protein and carbohydrate are excluded from 

 the food. The problems associated with mineral deficiency must 

 also be left aside except in so far as incidental reference requires. 

 Mineral metabolism is still on speculative ground, but we know of 

 no clear case of s])ecific disease arising through any but the 

 grossest omission of essential inorganic constituents. 



Theoretically, any mineral constituent required in the con- 

 struction of any animal tissue must of course be present in the 

 food in adequate amount, and insufficiency may give rise to a 

 generalised malnutrition, or to a specific set of pathological symp- 

 toms clinically recognisable as a specific disease, or to both. As 

 a passing example of the efifects of gross omission of an 

 important mineral constititent from a diet, we may quote the 

 following figtu"es* of some recent feeding experiments where 

 maize grain, which is notably deficient in calcium salts, was used 

 as main component of the food. 



I. Calcium-rich Diet. 2. Calcium-poor Diet. 



90 per cent. Maize. .Same diet without chalk. 



10 per cent. Gluten Meal, plus chalk 



fCaO = 0.448 per cent.) ( CaO = 0.055 per cent.) 



* Weiser. Biocliciii. Zeitschr.. July, 1914. 



