THE CHEMISTRY OF FOOD . 83 



18. Fibrin is derived from meats, and exists in the blood 

 both of man and the lower animals. Gluten, or vegetable 

 fibrin, resembles closely true fibrin, and is abundantly furnished 

 in wheat and other grains from which flour is commonly made. 

 Animal fibrin coagulates spontaneously when it is removed 

 from the body, and thus causes the " clotting " of the blood. 



19. Caseine is the curdy ingredient of the milk, and a highly 

 important food-substance. Its coagulation in milk takes place 

 not from heat, but by the addition of an acid, and also when 

 milk becomes sour from exposure to the air. It is commonly 

 effected, however, by introducing a piece of rennet, a prepara- 

 tion made from a calf's stomach. The curds, or caseine, may 

 then be separated from the ivhey, and made into cheese, by 

 pressing it sufficiently to drive off the water. 



20. The Fats or Oils. This is the second group of organic 

 foods. Those which are more solid are called fats; the more 

 fluid ones are the oils. Oleaginous substances are supplied in 

 both animal and vegetable food; but, from whatever source 

 derived, they are chemically much alike. They are insoluble 

 in water, and yet they unite readily with the watery fluids of 

 the body, and are by them conveyed to its various parts for 

 their nourishment. This is due to their property of " emulsi- 

 fying ; " that is, they are held in suspension, in a finely divided 

 state, in water. Ordinarily milk is an example of an emulsion. 



condition of the body ; and that food which keeps up the weight has been 

 regarded as satisfactory and nutritious. But this is not always a safe 

 judgment, owing to the property in water from innutritious food to make 

 good the loss of w.eight caused by the withdrawal of albumen and fat. 

 The weight may remain the same, while we are 4 losing flesh.' Fat, 

 also, may increase in badly nourished people, while the more essential 

 element of albumen is diminishing ; the fact being that the badly fed are 

 not always lighter than those who are well nourished. And further, the 

 feeling of satisfaction after eating is deceptive ; the Irish peasant who 

 consumes ten pounds of potatoes in a day feels quite satisfied, but is in 

 reality badly nourished by his diet containing three-fourths water." 

 Prof. Voitj of Munich. 



18. Fibrin, gluten, clotting of the blood ? 



19. Caseine ? Its coagulation ? Effect of rennet ? Making of cheese ? 



20. What are the fats ? The oils ? How supplied ? How alike ? Emulsifying ? Ex- 

 ample ? How do we know it ? 



