THE WORK OF LEAVES 171 



cottonseed oil (which gives little or no acid reaction 

 to litmus on being shaken up with a little alcohol 

 and water) and allowed to stand a few hours, the 

 oil will give an acid reaction, due to the fact that 

 the lipase of the Castor-bean has split the oil into 

 glycerine and fatty acids, which latter react with the 

 litmus in the presence of alcohol and water. 



Proteids are acted upon in the animal body by 

 both the gastric juice of the stomach arid the pan- 

 creatic juice of the small intestine. The first con- 

 tains a ferment, pepsin, which acts only in acid 

 solutions, the second a ferment, trypsin, which acts 

 only in neutral or alkaline solutions. 



Obtain a pig's stomach: dissect off some of the 

 inner lining, cut it up into small pieces with scissors 

 and pound it in a mortar with water and a little 

 glycerine. Filter the fluid, 1 and add to it pure strong 

 hydrochloric acid in the proportion of 1 cc. of acid 

 to 150 cc. of liquid. In this place a little fibrin 2 or 



1 Pepsin (obtainable at drug-stores) may be dissolved in water in the pro- 

 portion of one-half gram to 50 cc. of water to make artificial gastric juice. It 

 is much better, however, to obtain a stomach for the experiment. 



2 Fibrin may be obtained in dry condition (at drug-stores), in which case it 

 should be softened by soaking in water, or better, in water containing about 1 

 cc. of hydrochloric acid in every 100 cc. Fibrin may be prepared from blood 

 (obtainable of butchers) by whipping it with a bundle of sticks or wires : the 

 stringy, elastic substance which collects on them is the fibrin : this is a proteid 

 substance (apply the test for proteids); wash it in water, what is its color? 

 To the fibrin is due the clotting of blood when wounds are made : it is very 

 quickly coagulated by sugar, hence the value of treating cuts, etc., by sprink- 

 ling them at once with sugar : other substances, e. g., iron chloride, have a 

 similar action. If a little blood be allowed to stand in an open bottle the fibrin, 

 together with the red corpuscles, collects into a clot, leaving a straw-colored 

 liquid which occupies about half the space : this is the serum : it is the serum 

 which fills a blister. Find out what you can regarding the composition of 

 blood. See any good text-book of physiology. 



