28 THE CARBOHYDRATE ECONOMY OF CACTI. 



alcohol, each time heating to boiling for 3 hours, filtered, and the residue 

 washed with hot alcohol. This procedure removed all alcohol-soluble 

 sugars. The alcohol was then distilled off at reduced pressure, a greenish- 

 brown gum remaining. To this was added hot water to dissolve the sugars ; 

 a considerable amount of oil (largely chlorophyll) was insoluble. A small 

 quantity, 0.2 gram, of blood charcoal greatly facilitated the filtration. With- 

 out the addition of the blood charcoal it was almost impossible to get a clear 

 solution on account of the clogging of the filter-paper by the fine oil particles. 

 In order to make negligible any loss of sugar by adsorption by the charcoal, 

 the same lot of Merck's blood charcoal was used throughout. 1 



As the amount of protein and tannin in the cactus is very small, it was 

 found inadvisable to clarify the sugar solutions with lead acetate. The 

 water from the clear aqueous solution was distilled off at reduced pressure 

 (75 and 35 mm.) in a tared flask, finally with the water-bath boiling. 

 The residual light-brown gum was weighed, dissolved in water, and the 

 solution made up to a definite volume. The sugars were then determined 

 as described below. The reducing sugars present were monosaccharide 

 hexoses and pentoses. The mixture was then hydrolyzed with hydrochloric 

 acid, using 5 c. c. normal acid solution for every 100 c. c. of the sugar solu- 

 tion and heating for 3 hours at 80. Repeated trials with longer heating 

 showed that the inversion was complete. By the use of invertine, the same 

 values of cupric reduction were obtained as with hydrochloric acid, indi- 

 cating that there was no maltose present. 



The mixture was neutralized carefully with sodium bicarbonate, made up 

 to a definite volume, and the sugars determined. This determination repre- 

 sents monosaccharide hexoses and pentoses and invert sugar. The sugar 

 solution was then fermented in order to remove all hexose sugars. For this 

 a fresh preparation of carefully washed bakers' yeast was used. To the 

 sterilized sugar solution was added the yeast, mixed with distilled water to 

 a thin paste, 0.25 gram pressed yeast per gram of original gum. The vessel 

 was stoppered with cotton and left at 30 to 35 for 30 to 40 hours. Sepa- 

 rate experiments with various mixtures of invert sugar and 1-arabinose and 

 1-xylose showed that by this procedure all hexose sugars present in the plant 

 were removed, while the pentoses remained unchanged. The mixture was 

 then filtered and distilled at reduced pressure in order to remove the prod- 

 ucts of fermentation. The residual gum was dissolved in a definite volume 

 of water and the sugars determined with the alkaline copper solution. 



For the estimation of the polysaccharides, 5 to 15 grams of the dry 

 material was hydrolyzed with 200 to 600 c. c. of 1 per cent hydrochloric 

 acid in a flask, with reflux condenser, in the boiling-water bath for 3 hours. 

 The mixture was filtered, washed thoroughly with hot water, the filtrate 

 neutralized carefully with sodium bicarbonate, and made up to a definite 



1 WOODYATT, R. T., and H. F. HELMIIOLTZ. The use of blood charcoal as a clearing 

 agent for urine containing glucose. Arch. Intern. Med., 7, 598-601, 1911. 



