Chap. XVI.] SECRETION, ABSORPTION, DIGESTION. 309 



Secretion, Absorption, and Digestion. I will first give 

 my observations and experiments, and then a summary of 

 the results. 



The Effects of Obfects containing Soluble Nitrogenous Matter. 



( 1 ) Flies were placed on many leaves, and excited the glands to 

 secrete copiously; the secretion always becoming acid, though not 

 so before. After a time these insects were rendered so tender that 

 their limbs and bodies could be separated by a mere touch, owing 

 no doubt to the digestion and disintegration of their muscles. The 

 glands in contact with a small fly continued to secrete for four 

 days, and then became almost dry. A narrow strip of this leaf 

 was cut off, and the glands of the longer and shorter hairs, which 

 had lain in contact for the four days with the fly, and those which 

 had not touched it, were compared under the microscope, and pre- 

 sented a wonderful contrast. Those which had been in contact 

 were filled with brownish granular matter, the others with homo- 

 geneous fluid. There could therefore be no doubt that the former 

 had absorbed matter from the fly. 



(2) Small bits of roast meat, placed on a leaf, always caused 

 much acid secretion in the course of a few hours in one case 

 within 40 m. When thin fibres of meat were laid along the margin 

 of a leaf which stood almost upright, the secretion ran down to the 

 ground. Angular bits of meat, placed in little pools of the secre- 

 tion near the margin, were in the course of two or three days much 

 reduced in size, rounded, rendered more or less colourless and 

 transparent, and so miich softened that they fell to pieces on the 

 slightest touch. In only one instance was a very minute particle 

 completely dissolved, and this occurred within 48 hrs. When only 

 a small amount of secretion was excited, this was generally ab- 

 sorbed in from 24 hrs, to 48 hrs.; the glands being left dry. But 

 when the supply of secretion was copious, round either a single 

 rather large bit of meat, or round several small bits, the glands 

 did not become dry until six or seven days had elapsed. The most 

 rapid case of absorption observed by me was when a small drop 

 of an infusion of raw meat was placed on a leaf, for the glands 

 here became almost dry in 3 hrs. 20 m. Glands excited by small 

 particles of meat, and which have quickly absorbed their own se- 

 cretion, begin to sex-rete again in the course of seven or eight days 

 from the time when the meat was given them. 



(3) Three minute cubes of tough cartilnije from the leg-bone of 

 a sheep were laid on a leaf. After 10 hrs. 30 ra. some acid secretion 

 was excited, but the cartilage appeared little or not at all aflTected. 

 After 24 hrs. the cubes were rounded and much reduced in size; 

 after 32 hrs. they were softened to the centre, and one was quite 

 liquefied; after 35 hrs. mere traces of solid cartilage were left; and 

 after 48 hrs. a trace could still be seen through a lens in only 

 one of the three. After 82 hrs. not only were all three cubes com- 

 pletely liquefied, but all the secretion was absorbed and the glands 

 left dry. 



