HOW DIGESTION IS INFLUENCED. 567 



potatoes or hard cheese. Again, all vegetable substances too much 

 matured, and therefore composed of cells having harder cell-walls, are 

 more difficult to digest, and hence require much cooking, and artificial 

 subdivision, to burst and break down the cells, and permit the diges- 

 tive juices to enter their interior, and act on their contents. Carrots, 

 turnips, cabbages, celery, artichokes, asparagus, and onions, may be 

 classed in this category. Even the cooking of flour, and of all other 

 amylaceous articles of diet, helps digestion in an extraordinary degree, 

 by bursting or swelling the fecula or starch grains. Large quantities 

 of adipose tissue, intermixed with muscular tissue, probably impede 

 the penetration of the gastric juice, and so render too fat meats, such 

 as pork, and also oily fish, as, for example, salmon, comparatively in- 

 digestible. It has been found that the flesh of animals living in a wild 

 state, is more digestible than that of the allied tame species, probably 

 owing to the more fatty muscular tissues of the latter. A large quan- 

 tity of fat, in the shape of fatty tissue, taken with other food, may 

 have the same effect of interfering with digestion ; but such fatty tissue 

 is far preferable to fat itself, and more easy of digestion, because it is 

 contained in areolar tissue, and is divided into minute spherules within 

 the fine adipose cells, so that the gastric juice percolates it with com- 

 parative facility. Hence suet and cooked fat are more digestible than 

 the melted fat derived from them, and swimming on the surface of 

 gravy. Pure solid fats having a granulated texture, especially cold 

 butter, the particles of which adhere together, as it were, only by cer- 

 tain points of contact, are more easily digested than the same fats 

 taken in a melted condition, such as oiled butter, in which the oleagi- 

 nous particles have completely coalesced. It is possible, also, that the 

 heating of fatty matters determines slight chemical changes, incon- 

 sistent with easy digestion. But perhaps the most objectionable effect 

 of fat, is that which occurs in certain processes of cooking, in which 

 it saturates heated or dried albuminoid, gelatinoid, or amylaceous sub- 

 stances, and so preoccupies their interstices, as to render them ex- 

 tremely difficult of penetration by the gastric juice, which is aqueous, 

 as in the case of buttered toast, or greasy hot dishes of any kind. 

 Moreover, owing to the high temperature in roasting or baking, the 

 substances above mentioned, as well as the fats themselves, sometimes 

 undergo peculiar chemical changes, by which acrolein, or other pyro- 

 genic compounds are perhaps developed. These latter conditions are 

 met with in the burnt parts of roasted joints, in over-roasted, baked, 

 or fried parts of the skin of poultry or of fish, and especially in greasy 

 and burnt pie-crust. 



It would seem that animal albuminoid substances, held in solution, 

 as in soups and broths, are not more easily digested than the same 

 substances in a solid form ; for the water requires to be almost en- 

 tirely absorbed, before the nutrient principles can be converted into 

 peptones. Hence, solid food, even in the case of many invalids, is 

 more suitable than bulky fluid food. It is said that dextrin, introduced 

 into the system, favors the digestion of albumen (Schiff) ; this affords 

 an illustration of the advantage of mixed diets. 



Too large a quantity of food, at any one meal, also renders digestion 



