38 



ANIMAL CHEMISTRY. 



perty of dissolving in that fluid. During \ 

 digestion, the gastric juice, when separated, I 

 is found to contain a free mineral acid, the ' 

 presence of which checks all further change. 

 That the food is rendered soluble quite inde- 

 pendently of the vitality of the digestive 

 organs has been proved by a number of the 

 most beautiful experiments. Food, enclosed 

 in perforated metallic tubes, so that it could 

 not come into contact with the stomach, 

 was found to disappear as rapidly, and to be 

 as perfectly digested, as if the covering had 

 been absent; and fresh gastric juice, out of 

 the body, when boiled white of egg, or mus- 

 cular fibre, were kept in contact with it for 

 a time at the temperature of the body, 

 caused these substances to lose the solid 

 form and to dissolve in the liquid. 



9. It can hardly be doubted that the sub- 

 stance which is present in the gastric juice 

 in a state of change is a product of the trans- 

 formation of the stomach itself. No sub- 

 stances possess, in so high a degree as those 

 arising from the progressive decomposition 

 of the tissues containing gelatine or chon- 

 drine, the property of exciting a change in 

 the arrangement of the elements of other 

 compounds. When the lining membrane 

 of the stomach of any animal, as, for ex- 

 ample, that of the calf, is cleaned by con- 

 tinued washing with water, it produces no 

 effect whatever, if brought into contact with 

 a solution of sugar, with milk or other sub- 

 stances. But if the same membrane be ex- 

 posed for some time to the air, or dried, and 

 then placed in contact with such substances, 

 the sugar is changed, according to the state 

 of decomposition of the animal matter, 

 either into lactic acid, into mannite and mu- 

 cilage, or into alcohol and carbonic acid; 

 while milk is instantly coagulated. An or- 

 dinary animal bladder retains, when dry, all 

 its properties unchanged; but when ex- 

 posed to air and moisture, it undergoes a 

 change not indicated by any obvious exter- 

 nal signs. If, in this state, it be placed in a 

 solution of sugar of milk, that substance is 

 quickly changed into lactic acid. 



10. The fresh lining membrane of the 

 stomach of a calf, digested with weak mu- 

 riatic acid, gives to this fluid no power of 

 dissolving boiled flesh or coagulated white 

 of egg. But if previously allowed to dry, 

 or if left for a time in water, it then yields, 

 to water acidulated with muriatic acid, a 

 substance in minute quantity, the decompo- 

 sition of which is already commenced, and 

 is completed in the solution. If coagulated 

 albumen be placed in this solution, the state 

 of decomposition is communicated to it, 

 first at the edges, which become translucent, 

 pass into a mucilage, and finally dissolve. 

 The same change gradually affects the 

 whole mass, and at last it is entirely dis- 

 solved, with the exception of fatty particles, 

 which render the solution turbid. Oxygen 

 is conveyed to every part of the body by the 

 arterial blood ; moisture is every where pre- 

 sent; and thus we have united the chief 



conditions of all transformations in the ani- 

 mal body. 



Thus, as in the germination of seeds, the 

 presence of a body in a state of decomposi- 

 tion or transformation, which has been 

 called diastase, effects the solution of the 

 starch that is, its conversion into sugar ; 

 so, a product of the metamorphosis of the 

 substance of the stomach, being itself in a 

 state of metamorphosis which is completed 

 in the stomach, effects the dissolution of all 

 such parts of the food as are capable of as- 

 suming a soluble form. In certain diseases, 

 there are produced from the starch, sugar, 

 &c., of the food, lactic acid and mucilage. 

 (24.) These are the very same products 

 which we can produce out of sugar by 

 means of membrane in a state of decompo- 

 sition out of the body ; but in a normal state 

 of health, no lactic acid is formed in the 

 stomach. 



11. The property possessed by many sub- 

 stances, such as starch and the varieties of 

 sugar, by contact with animal substances in 

 a state of decomposition, to pass into lactic 

 acid, has induced physiologists, without 

 farther inquiry, to assume the fact of the 

 production of lactic acid during digestion 

 and the power which this acid has of dis- 

 solving phosphate of lime has led them t< 

 ascribe to it the character of a general sol 

 vent. But neither Prout nor Braconno 

 could detect lactic acid in the gastric juice, 

 and even Lehmann (see his " Lehrbuch der 

 Physiologischen Chemie," torn. i. p. 285) 

 obtained from the gastric juice of a cat only 

 microscopic crystals, which he took for lac- 

 tate of zinc, although their chemical cha- 

 racter could not be ascertained. The pre- 

 sence of free muriatic acid in the gastric 

 juice, first observed by Prout, has been con- 

 firmed by all those chemists who have ex- 

 amined that fluid since. This muriatic acid 

 is obviously derived from common salt, the 

 soda of which plays a very decided part in 

 the conversion of fibrine and caseine into 

 blood. 



Muriatic acid yields to no other acid in 

 the power of dissolving bone earth, and 

 even acetic acid, in this respect, is equal to 

 lactic acid. There is consequently no proof 

 of the necessity of lactic acid in the diges- 

 tive process ; and we know with certainty, 

 that in artificial digestion it is not formed. 

 Berzelius indeed has found lactic acid in the 

 blood and flesh of animals ; but when his 

 experiments were made, chemists were 

 ignorant of the extraordinary facility and 

 rapidity with which this acid is formed 

 from a number of substances containing its 

 elements, when in contact with animal 

 matter. 



In the gastric juice of a dog, Braconnot 

 found, along with free muriatic acid, distinct 

 traces of a salt of iron, which he at first 

 held to be an accidental admixture. But in 

 the gastric juice of a second dog, collected 

 with the utmost care, the iron was again 

 found. (Ann. de Ch. et de Ph. lix. p. 249. 



