Töpfer's Method for Total Acidity.--In an evaporating dish or small beaker (an "after-dinner" coffee-cup is a very convenient substitute) take 10 c.c. filtered stomach-contents and add three or four drops of the indicator, a 1 per cent. alcoholic solution of phenolphthalein. When the quantity of stomach fluid is small, 5 c.c. may be used, but results are less accurate than with a larger amount. Add decinormal solution {224} of sodium hydroxid drop by drop from a buret, until the fluid assumes a rose-red color which does not become deeper upon addition of another drop (Plate X, A, A'). When this point is reached, all the acid has been neutralized. The end reaction will be sharper if the fluid be saturated with sodium chlorid. A sheet of white paper beneath the beaker facilitates recognition of the color change. In clinical work the amount of acidity is expressed by the number of cubic centimeters of the decinormal sodium hydroxid solution which would be required to neutralize 100 c.c. of the gastric juice, each cubic centimeter representing one _degree_ of acidity. Hence multiply the number of cubic centimeters of decinormal solution required to neutralize the 10 c.c. of stomach fluid by ten. This gives the number of degrees of acidity. The amount may be expressed in terms of hydrochloric acid, if one remember that each degree is equivalent to 0.00365 per cent. hydrochloric acid. _Example_.--Suppose that 7 c.c. of decinormal solution were required to bring about the end reaction in 10 c.c. gastric juice; then 7 X 10 = 70 _degrees_ of acidity; and, expressed in terms of hydrochloric acid, 70 X 0.00365 = 0.255 _per cent._ Preparation of decinormal solutions is described in text-books on chemistry. The practitioner will find it best to have them made by a chemist, or to purchase from a chemic supply house. [Illustration: PLATE X. A, Gastric fluid to which a 1 per cent. solution of phenolphthalein has been added; B, gastric fluid to which a 1 per cent. solution of alizarin has been added; C, gastric fluid to which a 0.5 per cent. solution of dimethylamido-azobenzol has been added; A', A after titration with a decinormal solution of sodium hydroxid; B', B after titration with a decinormal solution of sodium hydroxid; C', C after titration with a decinormal solution of sodium hydroxid (Boston).] * * * * * (2) Hydrochloric Acid.--After the Ewald and Boas test-breakfasts, the amount of free hydrochloric acid varies normally between 25 and 50 degrees, or about 0.1 to 0.2 per cent. In disease, it may go considerably higher, or may be absent altogether. When the amount of free hydrochloric acid is normal, organic disease of the stomach probably does not exist. _Increase_ of free hydrochloric acid above 50 degrees {225} (_hyperchlorhydria_) generally indicates a neurosis, but also occurs in most cases of gastric ulcer and beginning chronic gastritis.