3OO ACTION UPON OTHER FOODS. 



ACTION UPON OTHER FOODS. 



Milk coagulates in the stomach, with the liberation of heat, as a 

 result of precipitation of the casein, which encloses the fat globules. 

 The free acid of the stomach is alone sufficient for precipitation, the 

 alkali being withdrawn from the casein, which it holds in solution. 



Hammarsten, in 1872, discovered a special rennet-ferment in the 

 gastric juice, which coagulates the casein in either neutral or alkaline 

 solutions. On this fact depends the preparation of cheese by means of 

 calf's stomach rennet. 



The rennet is formed in the chief cells of the gastric glands from a rennet-forming 

 substance, by the action of an acid. The rennet-forming substance is present 

 in the mucous membrane in much larger amount than rennet itself. One part 

 of rennet-ferment is capable of precipitating 800,000 parts of casein. The addition 

 of calcium chlorid hastens, while water retards, coagulation. An excess of alkali 

 impairs the activity of rennet. The rennet-ferment is best assisted by hydro- 

 chloric acid, followed, in order, by lactic, acetic, sulphuric and phosphoric acids. 



The casein, as well as the nucleo-albumin, is converted in the process of diges- 

 tion, mainly into peptone rich in phosphorus; a residue poor in phosphorus, para- 

 nuclein, remaining as an insoluble product. 



The rennet-ferment is destroyed by long-continued artificial digestion. To 

 obtain rennet, Hammarsten agitates artificial gastric juice prepared from the calf's 

 stomach, and after neutralization, with magnesium carbonate. The filtrate contains 

 only rennet, which, after acidulation with acetic acid, is precipitated by the in- 

 troduction of liquid stearic acid, to which it adheres. The acid is dissolved in 

 ether, which can then be readily separated. 



Finally, sugar of milk is converted in the gastric juice into lactic 

 acid, by fermentative activity lactic-acid ferment. Further, the milk- 

 sugar in the stomach and intestines is, in part, transformed into grape- 

 sugar. 



Cane-sugar is gradually converted into grape-sugar, in which process, 

 according to Uffelmann the gastric mucus, according to Leube the 

 gastric acid, plays the most important part. 



ACTION ON THE DIFFERENT TISSUES AND THEIR CONSTITUENT 



MATERIALS. 



( i) The gelatin-yielding substance of the various supporting structures connec- 

 tive tissue, fibrous cartilage and the matrix of bone as well as glutin itself, is pep- 

 tonized and digested in the gastric juice. (2) The structureless membranes (mem- 

 branae propriae) of the glands, sarcolemma, the nerve-sheath of Schwann, the 

 capsule of the crystalline lens, the elastic layers of the cornea, the membranes of 

 the fat-cells, are likewise digested, but scarcely the elastic, fenestrated membranes 

 and fibers. (3) Striated muscular tissue forms after digestion of the sarcolemma 

 and breaking up of the transversely striated contents into discs and fragments of 

 fibrils, as well as unstriated muscular tissue, a true digested peptone, in consequence 

 of hydration and the decomposition of the myosin. Remains of meat, however, 

 always pass over into the intestine. (4) The proteid elements of the soft cellular 

 structures of the glands, stratified epithelium, endothelium and lymphoid cells, are 

 converted into peptone, while the nuclein of the nuclei cannot, apparently, be 

 digested. (5) The horny portions of the epidermis, nails, hairs, as well as the chitin 

 and the wax of lower animals, are indigestible. (6) The erythrocytes are digested, 

 the hemoglobin decomposed into hematin and a globulin -like substance. The 

 latter is peptonized; the former remains unchanged, and in part appears in the 

 feces, and in part is absorbed and transformed into the coloring-matter of the bile. 



(7) The fibrin is easily digested into propeptone and fibrin-peptone by the taking up 

 of water and the breaking up of the molecule. Mucin is digested in the stomach. 



(8) Of vegetable articles of food, vegetable fats are not changed by the gastric 

 juice. The vegetable cells give up their protoplasmic contents for the production 

 of peptone, while the cellulose of the cell-walls is undigestible in the stomach of 

 human beings. 



