172 PHYSIOLOGICAL CHEMISTRY 



Spencer's Method. 1 (a) Prepare five reagent tubes, Nos. i, 2, 3, 4, and 5; more 

 if desired. 



To tubes i and 2 add 0.5 c.c. of gastric contents (filter if cloudy). 



(b) To tubes 2, 3, 4, and 5 add 0.5 c.c. of distilled water. 



(c) From tube 2 remove 0.5 c.c. of its mixed contents and add to tube 3. Mix 

 thoroughly and add 0.5 c.c. from tube 3 to tube 4. Repeat for tube 5. 



We now have dilutions of gastric contents of i, ^, ^, ^, and KG- 



(d) To each tube add one drop of phenolphthalein solution (phenolphthalein 

 i gram; alcohol (95 per cent) 100 c.c.); then add drop by drop a 2 per cent sodium 

 carbonate solution until a light pink color is produced. 



(e) To tubes i, 2, 3, and 4 add 0.5 c.c. of casein solution. Tube 5 must receive 

 i c.c. of casein solution, since it contains i c.c. of the diluted gastric contents. For 

 the casein solution, dissolve 0.4 gram of casein in 40 c.c. of N/io NaOH. Add 130 

 c.c. of distilled water, then 30 c.c. of N/io HC1. This leaves the solution alkaline 

 to the extent of 10 c.c. of N/io NaOH, minus about 3 c.c. neutralized by the 

 casein. 



(/) Incubate for five hours at 40 C. 



(g) Precipitate the undigested casein by dropwise addition of a solution of the 

 following composition: glacial acetic acid i c.c., alcohol (95 per cent) 50 c.c., dis- 

 tilled water 50 c.c. The tubes in which digestion has been complete remain clear; 

 others become turbid. 



(h) The tryptic values are expressed in terms of dilution. Thus, complete 

 digestion in tube 3 (a dilution of y) shows four times the tryptic power of un- 

 diluted gastric juice; taken as a standard as i, therefore, its tryptic value is 4. 



(i) Controls of boiled gastric contents plus casein solution, and of distilled water 

 plus casein solution, treated as above stated, must show no digestion, and become 

 turbid on addition of the precipitating solution. 



(e) Detection of Lactic Acid. When the acidity of the stomach 

 contents is reduced to a low value there may occur considerable fermen- 

 tation of carbohydrates which have been introduced into the stomach 

 in the ingested food. This fermentation yields various organic acids 

 among which lactic acid is particularly prominent. It is important, 

 therefore, in case of low gastric acidity that the stomach contents be 

 examined for lactic acid. 



Tests, i. Ether-Ferric Chloride Test (Strauss). A satisfactory 

 deduction regarding the presence of lactic acid can only be made by 

 removing the lactic acid from disturbing factors (e.g., hydrochloric acid, 

 protein digestion products, etc.) present in the stomach contents. 

 Lactic acid may be extracted from the stomach contents by ether. 

 The following technic not only serves to detect lactic acid but also gives 

 an approximate idea as to the amount of the acid present. 



Procedure. Introduce 5 c.c. of strained stomach contents into a small grad- 

 uated separately funnel, add 20 c.c. of ether and shake the mixture thoroughly. 



Elaborated by Dr. W. H. Spencer (Jour. Biol. Chem., 21, -165, 1915) in the author's 

 laboratory for the specific purpose of determining trypsin in gastric juice. For other tryp- 

 sin methods see Chapter X. . V 



