92 THE LACTIC ACID GROUP. 



present) we must boil it strongly, filter it, and, after concentrating 

 it, place on it a small zinc bar. Since, as we have already mentioned, 

 lactate of copper is far more soluble in water than lactate of zinc, 

 the zinc very soon becomes covered with white crystals of lactate 

 of zinc, if the fluid be sufficiently concentrated, and these crystals, 

 if they be allowed to remain for some time, may usually be easily 

 measured under the microscope. Distinct crystalline forms may 

 even be distinguished with the naked eye. If, however, in conse- 

 quence of the want of a Goniometer, an accurate crystallometric inves- 

 tigation cannot be instituted, we must precipitate the solution of the 

 zinc-salt with a boiling solution of protochloride of tin, and allow 

 it to stand for some time ; on then making a microscopic exami- 

 nation, we shall find clusters of crystals whose groups are composed 

 of thick rhombic tablets lying close upon one another. When we 

 have in this way prepared and explored the different lactates, (and 

 after some practice, tolerably small quantities are sufficient for this 

 purpose,) we hardly require to make an elementary analysis or to 

 determine the atomic weight, to enable us to decide regarding the 

 presence of lactic acid. 



Physiological Relations. 



Occurrence. The doubts regarding the nature of the free acid 

 of the gastric juice have given rise to a great number of investiga- 

 tions on this point. Prout* and Braconnott believed that their 

 experiments showed that the gastric juice contained no lactic acid, 

 but only hydrochloric acid. Subsequently, I thought that I had 

 satisfactorily provedj the existence of lactic acid in the gastric juice 

 of various carnivorous and herbivorous animals, ( by obtaining from 

 it several of the lactates, and referred the occurrence of free hydro- 

 chloric acid simply to the decomposition of the metallic chlorides 

 by the lactic acid during the evaporation or distillation of the 

 gastric juice. Hiinefeld supported this view. A period now arrived 

 when Liebig totally denied that lactic acid occurred in any of the 

 animal fluids, and, consequently, in examining the gastric juice of a 

 criminal immediately after he had been beheaded, Enderlin || was just 

 as unable to detect lactic acid, as he has been to find carbonate of 

 soda in the blood-ash. Blondlot,^[ also, in examining pure gastric 



* Phil. Trans, for 1824, p, 45. 

 t Ann. de Chim. T. 59, p. 348. 



J First edition of this work, 1840. Bd. 1, S. 284. Bericht uber d. Fortschritte der 

 physiol. u. path. Ch. im J. 1842. Leipzig. S. 10. 

 Chemie u. Medicin. Bd. 2, S. 81 ff. 

 || Ann. d. Ch. u. Pharm. Bd. 46, S. 123. 

 T[ Traite analytique de la Digestion. Paris et Nancy. 1843. p. 244. 



