ADVANCED PHYSIOLOGICAL CHEMISTRY 445 



an active and an inactive molecule. There are accordingly three lactic 

 acids, and two of these, viz., the inactive and dextrorotatory occur in 

 the body. The former of these is produced by the fermentation of 

 lactose (see Milk), and the latter is sarcolactic acid. 



There are two important chemical reactions for both forms of lactic 

 acid. The one is U/elmann's reaction (see p. 188). The other consists 

 of the fact that their zinc and calcium salts crystallise in small four-sided 

 prisms, and their calcium salts in fine needles arranged in clusters 

 (Fig. 271). 



The amount of lactic acid increases very much during the death of 

 the muscle, and it is also said to be increased in amount by muscular 

 activity. It must be remarked, however, that in order to demonstrate 

 a distinct increase after muscular contraction, it is necessary to subject 

 the muscle to prolonged stimulation, and that, after this, the death of 

 the muscle is accelerated. It is probably from the proteid, and not, as 

 was at one time supposed, from the glycogen that the lactic acid is 

 derived. 



Carnic Acid. If a weak solution of ferric chloride be added to a 

 muscle extract (from which the proteids have been removed by boiling 

 and the phosphates by the addition of calcium chloride and ammonia) 

 a brown precipitate is obtained. This is called Carniferrin, and 

 consists of the iron salt of a body called phospho-carnic acid. If, 

 further, the phosphoric acid and iron be split off from this we obtain 

 carnic acid, and this, curiously enough, has the same formula as, and 

 gives nearly all the reactions of, anti-peptone. 



CHAPTER VII. 

 DIGESTION. 



Gastric. The Acidity of the Gastric Juice. Besides Giinzberg's test 

 for free mineral acid, there remains another very delicate one known 

 as the Tropaeolin test. 



Place a drop of a saturated solution of Tropaeolin 00 in 94 per cent, 

 methylated spirit on a white slab, and dry it with moderate heat 

 (40 C.). To the still warm, dry, yellow stain which remains apply a 

 drop of the filtered gastric juice. A blue violet colour is produced 

 if free hydrochloric acid be present. The reaction is obtained with 

 other mineral acids besides hydrochloric, but only if these be present 

 in considerable amount. 



It must be noted that a negative result with either Giinzberg's 



