208 ANNUAL OP SCIENTIFIC DISCOVERY. 



untouched. The latest opponent we have to name is Mr. Savory, 

 who recently presented a paper before the Royal Society, entitled, Ex- 

 periments on Food ; its Destination and Uses. 



Liebig's theory may be briefly stated thus : Animals require food 

 to build up the fabric, and keep up the temperature of their bodies. 

 The plastic, or tissue-making food, is furnished by certain organic sub- 

 stances which contain nitrogen, and only by these ; it is therefore 

 called, indifferently, either nitrogenous, or tissue-making food. The 

 heat-making food is furnished by certain organic substances destitute 

 of nitrogen ; it is therefore called, indifferently, either non-nitrogenous 

 or calorifacient food. Albuminous substances, rich in nitrogen, form 

 the animal fabric ; carbonaceous substances, fats, oils, starch, sugars, 

 alcohol, etc., are quite incapable of forming any part of the animal 

 fabric, and are used as so much fuel, which is burned in the body to 

 keep up the temperature. 



The theory is thus here re-stated, simply with a view to enable our 

 readers to better appreciate the experimental results arrived at by 

 Mr. Savory. He fed animals upon different diets, taking particular 

 note of the weight, temperature, and general condition of the animals. 

 In one class, they were fed on a non-nitrogenous diet, consisting of 

 equal parts, by weight, of arrow-root, sago, tapioca, lard, and suet ; in 

 this mixture there was only a slight fraction of nitrogen, (.22 per cent.) 

 In another class, the diet was nitrogenous, with only a small amount of 

 fat, (1.55 per cent.) In the third class, the diet was mixed. What 

 were the results ? These : 



Nitrogenous materials are not only heat-making, but, under some 

 circumstances, .suffice alone to maintain the requisite temperature. 

 [This is in perfect accordance with the results obtained by Bischoff 

 and Voit.j 



It is in the highest degree probable, that under certain circumstan- 

 ces, nitrogenous materials may prove directly heat-making, without 

 previously forming tissue. Although life cannot be maintained with- 

 out nitrogenous food, no matter how abundantly the other kinds are 

 supplied, life, and even health and the normal temperature, can be 

 maintained upon a diet almost exclusively nitrogenous. 



Finally, " in these experiments the significant fact appeared, that 

 while the weight, strength, and general condition of the animals varied 

 very widely under the different diets to which they were subjected, 

 no considerable fluctuation teas observed in their temperature. Even 

 the slight variation from time to time recorded, seemed rather to result 

 from other causes, than to depend directly on the food." 



It is unnecessary to point out the irreconcilable contradiction be- 

 tween Liebig's theory, and such facts. We will only add in conclu- 

 sion, that Liebig's theory was not founded on any precise investigations, 

 but was simply a deduction from certain chemical premises, supported 

 by random facts drawn from the reports of travellers, the observa- 

 tion of a few countries, and such-like sources. The theory had so 

 plausible an air that the illustrative facts seemed merely required 

 to render it popularly intelligible, and not to serve as proofs. But a 

 rigorous scrutiny of the theory detects its initial mistake, a rigorous 

 confrontation with facts exposes its want of solid basis. 



