230 ANIMAL AMIDES. 



have been determined, and for which we are chiefly indebted to 

 Dr Schwann : 



1. When the pepsin solution is neutralized by potash, nothing 

 is precipitated ; but its digesting properties are destroyed. 



2. Though the pepsin solution be much diluted with acidulat- 

 ed water, its digesting powers are not injured, but it cannot be 

 diluted with pure water without the destruction of these powers. 



3. The quantity of acid necessary for the digestive properties 

 of the liquid continuing, is regulated not by the pepsin present, 

 but by the water. The muriatic acid of commerce present must 

 amount to 2J per cent. 



4. When food is dissolved in this acidulated liquor, none of 

 the acid is saturated. The quantity still uncombined is the same 

 as at first. 



5. If we neutralize the solution, evaporate it to dryness in a 

 low temperature, and digest the residue in alcohol, the digestive 

 properties are destroyed. 



6. If the pepsin liquor be heated to the boiling point, its di- 

 gestive properties are destroyed. 



7. When acetate of lead is dropt into the pepsin solution, the 

 pepsin is precipitated in combination with the oxide of lead, and 

 the precipitation is more complete if the liquor has been previous- 

 ly neutralized. Pepsin is precipitated also from its neutral so- 

 lution by corrosive sublimate, but not by prussiate of potash. 



8. But the most characteristic action of pepsin is its coagulat- 

 ing milk, and throwing down the casein. When one part of pep- 

 sin solution is mixed with 238 parts of milk, the whole is coagu- 

 lated. The quantity of muriatic acid of commerce necessary to 

 produce the same effect is 3-3 per cent. 



The neutralized pepsin solution still coagulates milk, but if its 

 temperature be raised to the boiling point, this property is de- 

 stroyed. 



9. Pepsin and casein may be reciprocally used as reagents for 

 each other. A liquid containing only 0-0625 per cent, of casein 

 is precipitated by the neutral pepsin solutions. This delicate ac- 

 tion on casein is the most characteristic property of pepsin 

 hitherto observed, and puts it in our power to distinguish it from 

 other substances, especially from mucus, with which, from some 

 of its properties, it might otherwise be confounded. 



10. The small quantity of pepsin which causes the solution of 



