FOOD 575 



Primitive peoples adopt such methods as smoking, saUing or 

 pickHng. 



Modern peoples, on the other hand, use such chemical materials 

 as sodium benzoate, salicylic acid, &c., which when present in food 

 in sufficient quantity to preserve it are tasteless, odourless, and can 

 onlv be known by the label or chemical analysis. 



The old-fashioned methods of salt and smoke had much in their 

 favour. 



It should not be forgotten that fresh meat can be kept for four to 

 six days as a result of boiling it slightly each morning. 



Meat preservation is all-important for the tropics and ocean 

 steamers. Some method of preservation is essential. 



The methods usually employed are (after Whitelegge and 

 Newman) : — 



(i) Exclusion of air. 



The meat may be dipped into boiling water, when the external 

 coagulated albumin forms an impervious layer, or it may be 

 coated by paraffin or fat. 



(2) Preservative Injections. 



Inject the blood-vessels with water, then with a solution of 

 common salt, or alum with aluminum chloride. 



(3) External Preservatives as : — 



Salt or brine, sugar, boric acid, weak carbolic acid, &c. 



(4) Pickles. 



Salt and a little potassium nitrate are mixed together and well 

 rubbed in. 



(5) Drying after exposure to smoke from a wood lire. 

 This is the favourite method of natives. 



(6) Refrigeration. 



The application of cold, just above freezing point, must be 

 continuous. Decomposition is rapid when the cold is with- 

 drawn if rigor mortis had set in before the freezing. 



(7) Sterilised Enclosures. 



Hermetically sealed in vessels in vacuo or in sterilized air. 

 The air is expelled previous to sealing by boiling, steam, 



chemicals, e.g., sodium sulphite, &c. 

 Imperfections in sterilization result in partial decomposition 

 of the contents and when ingested of toxic symptoms in the 

 consumer. 

 The dangers from tinned foods are from : — 

 (i) Added preservatives in excess. 



(2) Colouring agents. 



(3) Salts of tin, lead and zinc from chemical reaction in the tin. 



(4) Absence of vitamines. 



