DIGESTION. 97 



The Alkalinity of the Alimentary Canal. 



At the time the article on the anatomy of the gypsy moth 

 was prepared it was noticed that the digestive fluids of the 

 larva were strongly alkaline ; but, while the fact seemed 

 quite suggestive, investigations of the cause of this alkalin- 

 ity were deferred until such a time as the assistance of a 

 chemist could be obtained. 



For a preliminary examination several full-grown cater- 

 pillars were killed by exposure to fumes of chloroform, and 

 the alimentary canal of each carefully removed and washed. 

 After maceration in water the material was subjected to a 

 careful analysis for both organic and inorganic bases and 

 acids, but nothing of an organic nature that could give an 

 alkaline reaction to the digestive fluids could be detected. 

 Repeated examinations of the water extract, however, showed 

 the presence of appreciable amounts of phosphoric acid and 

 potassium, with traces of calcium and magnesium. It is 

 well known that the phosphates of potassium and sodium 

 give an alkaline reaction with litmus, and, since the presence 

 in the digestive fluid of comparatively large quantities of 

 potassium and phosphoric acid was proven^ it was apparent 

 that the alkalinity of this fluid is due to the presence of a 

 phosphate of potash. 



Having thus determined qualitatively the source of the 

 alkalinity, it seemed desirable to make a quantitative analysis 

 of the digestive systems of a number of larvae, in order to 

 obtain an accurate idea of the amount of phosphates of potash 

 occurring in each insect. For this purpose the following 

 method was adopted : the alimentary canals of sixty-six 

 larvae were carefully removed, washed and macerated in water, 

 as in the previous analysis, and, it having been found that 

 the albuminous substances contained in the material seriously 

 interfered with filtration, resort was made to dialysis, with 

 good results. The macerated material was placed in a 

 dialyzing apparatus and suspended in a dish containing a 

 large quantity of freshly distilled water, the whole being 

 kept at a cool temperature, and the water in the dish replaced 

 with a fresh supply at intervals of twelve hours each for 

 seventy-two hours. At the end of this time the water taken 



