Chap. VI. DIGESTION. 95 



cubes of albumen of the same size as those above used, left for 

 seven days in a little hydrochloric acid of the above strength, 

 retained all their angles as perfect as ever. 



Experiment 8. — Cubes of albumen (of -^ of an inch, or 2-54: 

 mm.) were placed on five leaves, and minute drops of a solu- 

 tion of one part of carbonate of soda to 437 of water were added 

 at intervals to three of them, and di'ops of carbonate of potash 

 of the same strength to the other two. The drops were given 

 on the head of a rather large pin, and I ascertained that 

 each was equal to about ^^ of a minim (-0059 ml.), so that 

 each contained only -^^ of a grain (-0135 mg.) of the alkali. 

 This was not sufficient, for after 46 hrs. all five cubes were 

 dissolved. 



Experiment 9. — The last experiment was repeated on four 

 leaves, with this difference, that drops of the same solution of 

 carbonate of soda were added rather oftener, as often as the 

 secretion became acid, so that it was much more effectually 

 neutralised. And now after 24 hrs. the angles of three of 

 the cubes were not in the least rounded, those of the fourth 

 being so in a very slight degree. Drops of extremely weak 

 hydrochloric acid (viz. one part to 847 of water) were then 

 added, just enough to neutralise the alkali which was still 

 present ; and now digestion immediately recommenced, so that 

 after 23 hrs. 30 m. three of the cubes were completely dis- 

 solved, whilst the fourth was converted into a minute sphere, 

 surrounded by transparent fluid; and this sphere next day 

 disappeared. 



Experiment 10. — Stronger solutions of carbonate of soda and 

 of potash were next used, viz. one part to 109 of water; and as 

 the same-sized drops were given as before, each drop contained 

 y^ of a grain (-0539 mg.) of either salt. Two cubes of albu- 

 men (each about J^ of an inch, or '635 mm.) were placed on the 

 same leaf, and two on another. Each leaf received, as soon as 

 the secretion became slightly acid (and this occurred four times 

 within 24 hrs.^ drops either of the soda or potash, and the acid 

 was thus effectually neutralised. The experiment now succeeded 

 perfectly, for after 22 hrs. the angles of the cubes were as sharp 

 as they were at first, and we know from experiment 5 that such 

 small cubes would have been completely rounded within this 

 time by the secretion in its natural state. Some of the fluid was 

 now removed with blotting-paper from the discs of the leaves, 

 and minute drops of hydrochloric acid of the strength of one 

 part to 200 of water was added. Acid of this greater strength 

 was used as the solutions of the alkalies were stronger. The 



