AN INVITATION TO DINNER. 345 



the element " nitrogen " in the processes of animal bodies cannot be 

 over-estimated. A high authority in foods makes the remark that 

 " wherever living changes are carried on, nitrogenised matter is 

 present." We further discover that the most vital substance of 

 animal frames the famous " protoplasm " itself is a nitrogenous 

 compound. A speck of this nitrogenous matter, having much the 

 same composition as the " albumen," or white of egg itself, may con- 

 stitute of itself a perfect living being. The animalcules of the stag- 

 nant pool are such jelly-specks ; and the living protoplasm whereof 

 the vital parts of our own frames are composed, exhibits a close 

 identity of composition with the matter which constitutes the whole 

 structure of lower life, the actual and visible entity of the higher 

 animals, and the vital substance of the plant world at large. It can 

 therefore be understood that with this living matter and compounds 

 of allied nature entering into the structure of our frames, we should 

 demand a continual supply of like substances in our food. At 

 Smith's repast we shall obtain substances rich in " nitrogenous " foods 

 for the renewal of our protoplasm or living tissues, from well-nigh 

 every substance set before us. The juice of meat found, for example, 

 in soups, the fibres of meat themselves, the gravies and sauces which 

 decorate the viands, the milk which forms an element in the repast, 

 the eggs and vegetables that in one form or another figure in the 

 ?nenu, and the fruits and cheese of the feast, each and all contribute 

 a proportion of the varied " nitrogenous " substances that go to form 

 the flesh and tissues of our bodies. 



Next in order come the fats and oils. At dinner, it is hardly 

 necessary to say, we obtain a due proportion of these substances in 

 very varied forms. It is true we do not emulate the nutritive exist- 

 ence of the Esquimaux, whose dietary of blubber and fats consti- 

 tutes the summum bonum of a life spent amid perpetual snow. But 

 the quantity of fatty matters we daily contrive to ingest in one form 

 or another is very considerable. From animal foods, the fats are 

 readily obtainable, and from vegetables, oils of various kinds are 

 also elaborated. The necessity for fat as an article of diet is seen 

 when we learn from physiology that it not merely conserves heat 

 a function seen in whales and fat persons generally but supplies 

 material when it passes into the blood which affords our bodily 

 fuel. Fats and oils are " heat-producers," and it is when the fat 

 of the blood and the oxygen inhaled into that fluid from the air 

 come into chemical combination, that heat is produced. It is 

 needless to add that this process is being continually carried on in 

 the human body, and to a greater or less degree in that of all other 

 animals. The " starches and sugars " form the final materials into 

 which we may resolve our dinner. A large variety of substances 

 figure in the lists of chemists under the above designation. Common 



