and allow a slow current of water to flow into the beaker, and to overflow. Arrange the apparatus as shown in Fig. 8. Care must be taken that the tap-water does not have access to the inside of the dialyzing tube. Allow the dialysis to proceed for some days, and at the end of this time replace the tap-water with distilled water. Allow the dialysis to go on for three days more, and replace the distilled water by fresh at least every day. Open the dialyzing tube over a beaker. The sides of the tube will be found covered with a white film of pure globulin. The globulin is not entirely insoluble in distilled water, and hence a certain amount will be found in the water taken out of the dialyzer.

Serum-albumin, which is found in blood-serum, is in many respects identical with egg-albumin. One of the reactions which serves to distinguish it from egg-albumin is its behavior with ether. When solutions of egg-albumin are shaken with ether the albumin is coagulated. Test a small quantity of serum-albumin by shaking it with ether. Does it coagulate?

The Alkalinity of the Blood.-Quantitative Estimation. This estimation has come into recent prominence as a clinical feature of examinations of cases of rheumatic and gouty affections in which the alkalinity of the blood has been found to be decreased.

The only special piece of apparatus needed is a pipette made after the model of the Thoma-Zeiss pipette used in hematocytometric estimations. This

pipette is made on a larger scale to contain up to the mark on the capillary tube 0.05 c. c. of blood. The bulb of the pipette contains about 2 to 3 c.c. The

N

solutions required are a solution of tartaric acid,

100

made by dissolving 0.75 gram of tartaric acid in 1000 c. c. of water. Each cubic centimeter of this solution corresponds to 0.0004 gram of sodium hydroxide, or 0.00053 gram of Na2CO,.

The blood is withdrawn from the finger by means of the pipette till it reaches the mark on the capillary tube. Distilled water is then drawn in till the bulb of the pipette is almost filled. The mixing of the blood solution is effected as in bloodcounting. The dilute solution of blood is then expelled into a small beaker, and the pipette washed out with a little distilled water. The solution of

N

blood is then titrated with the tartaric acid in

100

the usual way, using strips of sensitive litmuspaper to show when the change in the reaction of the blood has taken place. As the amount of blood which has been used is 0.05 c. c., the amount of tartaric acid used must be multiplied by 20 to give the alkalinity of 1 c.c. of blood.

Example.-Took 0.05 c.c. of blood, diluted with

water, and titrated with

N

100

tartaric acid. Used

1.9 c.c. of the acid solution. Hence, 1.9 X 0.0004

0.0076 NaOH in 0.05 c.c. of blood. Therefore, 0.0076 X 20 = 0.0156 amount of NaOH equivalent to the akalinity of 1 c.c. of blood.

56 Digestive fluids, prODUCTS OF DIGESTION.

THE DIGEStive fluids, AND THE PRODUCTS OF DIGESTION.

The Saliva.-The saliva as collected from the mouth is a mixture of the secretion of the parotid, submaxillary, and sublingual glands. The amount secreted in the twenty-four hours is estimated at 1500 c.c. It contains about 0.5 per cent. of solid matter, which consists chiefly of serum-albumin, mucin, and the ferment ptyalin, as the organic part; and sodium bicarbonate and potassium sulfocyanid as the inorganic part. The former salt is of interest, as giving the alkaline reaction to the saliva, and also as being transformed into sodium carbonate and carbon dioxid when saliva is allowed to stand.

The potassium sulfocyanid is secreted by the parotid gland alone.

The functions of the saliva are, first, to furnish sufficient water to mix with the solid food-materials, in order to render them fluid-in a state to be acted upon by the gastric and pancreatic juices; secondly, to convert some of the starchy material into soluble compounds, of which dextrins, maltoses, and glucose are the chief.

Saliva for the following tests may be obtained by first rinsing the mouth with water, and chewing a piece of paraffin-wax for a few minutes. The nerves supplying the glands are stimulated, and a copious supply of saliva results. The character of

the secretion of the different glands seems to vary, and their action on starch is also connected with

the presence of micro-organisms, so that a perfectly sterile saliva, such as has been obtained by canalizing the ducts under perfectly aseptic conditions, has been found to be without action on starch. With the advent of micro-organisms from the air the fluid regained its diastatic power.

Make a solution of soluble starch by heating I gram of starch powder with 100 c.c. of water.

I. TO IO c. c. of the starch solution warmed to 40° C. add I c. c. of saliva. Note an almost instant clearing of the mixture. To a few cubic centimeters of the resulting fluid add a drop of iodin solution. Note that the color is brown, or even faintly yellow. Compare the color with that obtained by treating an equal amount of the original starch solution with a drop of iodin solution.

2. Heat a few cubic centimeters of saliva to boiling. Test the power of the solution on cooling to clear a starch solution. Is the starch converted into dextrins and maltoses by the boiled saliva?

3. Treat I c. c. of saliva with a drop of hydrochloric acid. Add a drop of dilute ferric chlorid. Note the formation of a red color, due to ferric sulfocyanid.

EXAMINATION OF THE CONTENTS OF THE

STOMACH.

The digestive fluid of the stomach is an almost clear liquid having a strong acid reaction. It is obtained either by means of the stomach-tube or through a permanent or temporary fistula. As

obtained from the stomach it is always mixed with saliva.

Unmixed with food materials it is essentially a solution of hydrochloric acid, containing about 0.3 per cent. of that compound, with pepsin, the proteolytic ferment of the stomach, and rennin, the milkcurdling ferment. As might be expected, the fluid always contains a large number of micro-organisms, which, with the exception of the lactic-acid bacillus and certain pathogenic microbes, favor the digestive process. The development of these micro-organisms is, however, inhibited by the amount of acid present in the normal gastric juice. If the amount of the hydrochloric acid be increased above normal, or especially if it be decreased in quantity below that present in health, the growth of the organisms is not only not impeded, but the gastric contents form an excellent culture-medium for them. The secretion of the gastric juice is not continuous, but is dependent on mechanical stimulation, and more particularly on the psychical factor. It is therefore more abundant before taking food, especially if the subject be hungry, and after the completion of a full meal. The degree of acidity of the juice and its digestive activity are also dependent on the quality of the food taken into the stomach. With the ingestion of proteids the acidity increases, while on a carbohydrate diet the acidity is least. The enzymes found in the contents of the stomach are two: Pepsin, the proteolytic ferment, and rennin, the milk-coagulating ferment.

Pepsin is found in the stomach of all vertebrates,