THE WORK OF LEA VES 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 pi-esence of alcohol and water. 



Proteids are acted upon in the animal body by 

 both the gastric juice of the stomach and 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, ^ 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^ or 



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

 portion of one-litilf 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 op6n 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. 



