244 PHYSIOLOGICAL CHEMISTRY 



Inasmuch as stools vary so greatly as to water content, it is essential to an 

 accurate comparison of stools that such comparison be made on the basis of the 

 solid matter. Supposing, for example, that in the above determination we had 

 6.2 c.c. of sediment. Since the supernatant fluid was removed and made up to 

 50 c.c. before testing its amylolytic value, it is evident that i c.c. of this sediment is 

 equivalent to 8.1 c.c. of extract. Therefore, in order to derive the amylolytic 

 value of i c.c. of sediment, we must multiply the value (16.1) as obtained above 

 for the extract, by 8.1. This yields 130.4 and enables us to express the activity 

 as follows: 



Df 3 2 ; = 130.4 



The above method of calculation is that suggested by Wohlgemuth. In case time 

 and facilities permit of the determination of the moisture content of the feces, it is 

 much more accurate and satisfactory to place the amylolytic values of the stools 

 on a " gram of dry matter " basis. The amylolytic values of the stools are expressed 

 as the number of cubic centimeters of i per cent starch solution which the amylase 

 content of i gram of dry feces is capable of digesting. 



22. Quantitative Determination of Fecal Bacteria. 1 The method is a simpli- 

 fication of MacNeal's adaptation of the Strasburger procedure. 2 About 2 grams of 

 feces are accurately weighed and placed in a 50. c.c. centrifuge tube. To the feces 

 in the tube a few drops of 0.2 per cent hydrochloric acid are added, and the material 

 is mixed to a smooth paste by means of a glass rod. Further amounts of the acid 

 are added with continued crushing and stirring until the material is thoroughly 

 suspended. The tube is then whirled in the centrifuge at high speed for one-half 

 to one minute. The suspension is found sedimented into more or less definite layers, 

 the uppermost of which is fairly free from the larger particles. The upper and 

 more liquid portion of the suspension is now drawn off by means of a pipette and 

 transferred to a beaker. 3 The sediment remaining in the tube is again rubbed up 

 with the glass rod with the addition of further amounts of dilute acid, and again cen- 

 trifugalized for one-half to one minute. The supernatant liquid is pipetted off and 

 added to the first, the same pipette being used for the one determination through- 

 out. 4 A third portion of the dilute acid is then added to the sediment, which is 

 again mixed by stirring and again centrifugalized. All the washings are added to 

 the first one, and during the process care is taken to wash the material from the 

 walls and mouth of the centrifuge tube down into it. Finally, when the sediment 

 is sufficiently free from bacteria, the various remaining particles are visibly clean, 

 and the supernatant liquid after centrifugalization remains almost clear. This is 

 removed to the beaker in which are now practically all the bacteria present in the 

 original portion of feces, together with some solid matter not yet separated. In the 

 centrifuge tubes there is a considerable amount of bacteria-free solid matter. 



The suspension is now transferred to the same centrifuge tube, centrifugalized 

 for a minute, and the supernatant liquid transferred to a clean beaker by means of 

 the same pipette. The tube is then refilled from the first beaker and thus all the 

 suspension centrifugalized a second time. The beaker is finally carefully washed 



1 Mattill and Hawk: Jour. Exp. Med., 14, 433, 1911. 



2 MacNeal, Latzer and Kerr, Jour. Inf. Dis., 6, 123, 1909. 



3 A 25 c.c. pipette is the most satisfactory size; to facilitate observation, the delivery tube 

 is bent near the bulb to an angle of about 120 degrees. 



4 A convenient support for the pipettes is a wire spring on a glass base, such as is used on 

 a desk for pen-holders. The delivery tube, just where it is bent, is inserted between the 

 wires, and any liquid not delivered collects in the bend of the tube. 



