OF DIGESTION. 365 



either. These nerves, however, are a main condition of digestion, and 

 they present themselves, especially, at the stomach and anterior stomach, 

 because it is the most active portion of the intestine in exercising the 

 function of digestion. Both comminute, especially the proventriculus, 

 the remainder of the intestine absorbs; a considerable interruption of the 

 function of digestion has consequently been observed in the superior 

 animals upon the scission of this nerve. 



In those insects which possess no proventriculus the digestion of the 

 food is effected less by comminution than by the gastric juice found in 

 the stomach. It also appears to be of an alkaline nature, at least 

 Ramdohr observed a fermentation upon the application of acid, and 

 according to Rengger it stains litmus paper of a brown red; and according 

 to the former it also turns paper blue which has been previously 

 stained red by an acid. Rengger's experiments upon the caterpillar of 

 Deilephila Euphorbia? most distinctly convince us of the purely che- 

 mical and dynamical transformation of the food in the stomach. The 

 form of the small bitten pieces of the leaf remains unchanged, but they 

 were somewhat loosened, and they appeared at the lower portion of the 

 stomach to have lost substance. The fluid contained within the stomach 

 was stained green by their extract. In other caterpillars, for example, 

 that of Pontia brassica, the chyme appeared more comminuted and 

 more pappy, doubtlessly because the substance of the leaf of the 

 cabbage is more juicy, softer, and more decomposable than that of the 

 Euphorbia. The separation and absorption of the chyme is promoted 

 by the constant peristaltic motion of the stomach : this motion inti- 

 mately intermixes the portions of the food, and gradually subjects them 

 equally to the action of the gastric juice secreted by the glands of the 

 stomach, and it partly helps to move the food from the anterior to the 

 posterior extremity of the stomach. It is here that the elaboration of 

 the food has attained its highest point, and it is therefore here that it 

 least resembles its original quality ; it has here become darker and 

 browner, whereas it was originally of almost the same colour as that of 

 the leaf of the plant. But the mechanical advance of the food is not 

 however wholly owing to the peristaltic motion, but it also depends upon 

 whether fresh food has been received. When this is not the case the 

 whole process of digestion appears more slow ; the food already in the 

 stomach then remains there, but becomes gradually softer and looser, 

 and loses its colour, and appears decomposing ; at least, according to 

 Rengger, it then smells very unpleasantly ; it also gradually loses the 



