SACCHARINE COMPOUNDS. 79 



composition and in most essential properties with that obtained from the fermen- 

 tation of sugar, differs from it in certain of the properties of the salts which it 

 forms with bases; and the acid of the juice of flesh has been recently distin- 

 guished as a lactic acid, whilst that obtained in the usual way (with which the 

 acid of the gastric fluid corresponds) is designated as b lactic acid. This distinc- 

 tion will be found to be of much importance, when we examine into the sources 

 of lactic acid in the animal economy. Much discussion has taken place at dif- 

 ferent times with regard to the existence of lactic acid in various parts of the 

 animal body, chiefly in consequence of the extreme difficulty of determining its 

 presence by ordinary chemical tests ; the production of some of its crystalline salts, 

 and the accurate measurement of the angles of these, being the only method on 

 which reliance can be placed. The following, according to Lehmann, may be 

 regarded as well-established facts, free from the errors of the earlier analyses. 



49. Lactic acid is a constant constituent of the gastric juice ; and as this is 

 true of carnivorous as well as of herbivorous animals, it cannot be looked on in 

 any other light than as a secretion from the blood. It is also found in the con- 

 tents of the small intestines, which, notwithstanding the neutralizing power of 

 the bile, usually exhibit an acid reaction ; but although its presence there may 

 be attributed to the admixture of the gastric solvent, yet, as it is found in much 

 larger amount in the small intestines of herbivorous than in those of carnivorous 

 animals, and as its proportion is increased in the former by the ingestion of fari- 

 naceous food, the excess would seem to be due to the direct transformation of 

 amylaceous matters in the alimentary canal. The acid reaction of the mucus 

 which lines the intestinal tube has been found to be due to lactic acid ; as is also 

 that which often presents itself in the contents of the large intestine, especially 

 when vegetable food has been ingested. Distinct evidence has been obtained of 

 the presence of lactic acid in the chyle of herbivorous animals, in which it is 

 obviously derived from the food; on the other hand, there are indications of its 

 existence in the lymph, where its presence must be rather attributed to its pro- 

 duction in the muscular substance. It seems impossible to demonstrate the 

 existence of lactic acid in healthy blood, by direct experiment; but, as Lehniann 

 remarks, a the simplest induction proves that it must be present there, even if it 

 only remains for a very short period;" since in no other way can it be under- 

 stood how the lactic acid introduced by the chyle, or generated in the muscular 

 substance, can find its way into the gastric, urinary, cutaneous, or other secre- 

 tions. The fact appears to be that, in the healthy state of the system, lactic 

 acid is decomposed by the respiratory process, or is eliminated from the blood 

 by the secretory operations, as fast as it finds its way into the circulation ; and 

 thus, as in the case of urea, it never accumulates in the blood to such a degree 

 as to make its presence evident, unless it be either introduced in undue propor- 

 tion, or its elimination be checked. It seems probable that when the blood pre- 

 sents an acid reaction, as happens in some diseases, this is to be attributed to an 

 excess of lactic acid ; since this substance, although not distinctly detected in 

 such blood, has been clearly made out in the fluids exuded from it. The rapidity 

 with which lactic acid is decomposed by the respiratory process (carbonic acid 

 being left, in combination with the basis), may be judged of by the fact that 

 within from five to thirteen minutes after considerable quantities of the alkaline 

 lactates have been introduced into the stomach, or have been injected into the 

 current of the circulation, the urine is found to be rendered alkaline by the pre- 

 sence of their carbonates. The existence of free lactic acid in the juice of flesh, 

 as long ago asserted by Berzelius, may now be considered as a certainty; and it 

 is probable that, as further maintained by Berzelius, the amount of free lactic 

 acid in a muscle is proportioned to the degree in which it had been previously 

 exercised. Now, that this lactic acid cannot have been generated by the direct 

 transformation of the elements of food, and merely attracted from the blood by 



