60 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



put the meat into boiling water at once, so that the outer part is 

 coagulated, and the loss of material minimised. 



An extremely important point in this connection is that beef tea 

 and similar meat extracts should not be regarded as foods. They 

 are valuable as pleasant stimulating drinks for invalids, but they 

 contain very little of the nutritive material of the meat, their chief 

 constituents, next to water, being the salts and extractives (creatine, 

 hypoxanthine, lactic acid, &c.) of flesh. 



Many invalids restricted to a liquid diet get tired of milk, and 

 imagine that they get sufficient nutriment by taking beef tea instead. 

 It is very important that this erroneous idea should be corrected. One 

 of the greatest difficulties that a physician has to deal with in these 

 cases is the distaste which many adults evince for milk. It is 

 essential that this should be obviated as far as possible by preparing 

 the milk in different ways to avoid monotony. Some can take 

 koumiss; but a less expensive variation may be introduced in the 

 shape of junkets, which, although well known in the West of 

 England, are comparatively unknown in other parts. The preparation 

 of a junket consists of adding to warm milk in a bowl or dish a small 

 quantity of rennet (Clark's essence is very good for this purpose) and 

 flavouring material according to taste. The mixture is then put 

 aside, and in a short time the milk sets into a jelly (coagulation of 

 casein), which may then be served with or without cream. 



Soup contains the extractives of meat, a small proportion of the 

 proteins, and the principal part of the gelatin, The gelatin is usually 

 increased by adding bones and fibrous tissue to the stock. It is the 

 presence of this substance which causes the soup when cold to 

 gelatinise. 



ACCESSORIES TO FOOD 



Among these must be placed alcohol, the value of which within 

 moderate limits is not as a food, but as a stimulant ; condiments 

 (mustard, pepper, ginger, curry powder, &c.), which are stomachic 

 stimulants, the abuse of which is followed by dyspeptic troubles; 

 and tea, coffee, cocoa, and similar drinks. These are stimulants 

 chiefly to the nervous system ; tea, coffee, mat6 (Paraguay), guarana 

 (Brazil), cola nut (Central Africa), bush tea (South Africa), and a 

 few other plants used in various countries all owe their chief pro- 

 perty to an alkaloid called theine or caffeine (C 8 H 10 N 4 0. 2 ) ; cocoa 

 to the closely related alkaloid, theobromine (C 7 H 8 N 4 2 ) ; coca to 

 cocaine. These alkaloids are all poisonous, and used in excess, even 

 in the form of infusions of tea and coffee, produce over-excitment, 



