COMPOSITION OF THE DIGESTIVE JUICES. [cH. VIII. 



(iii.) Examine the crystalline deposit in A, or, failing this, the 

 mass in B. Under the lower power of the microscope, tyrosine will 

 appear as sheaves or fan-shaped aggregates of needles. The material 

 in B may also contain spheres or cones with a radiating striation 

 consisting of leucine. Should these not be found, the crystalline 

 mass should be filtered off by use of a suction pump and the filtrate 

 concentrated on a boiling water bath. On standing for 24 hours 

 the characteristic leucine balls will separate out. 



G. Erepsin. 



This is a proteolytic enzyme widely distributed in the 

 animal and vegetable kingdoms. In animals it is especially 

 abundant in the mucous membrane of the intestine, 

 particularly in the jejunum. It is found in the succus 

 entericus. 



It differs from trypsin in that it has no action on such 

 native proteins as albumins and globulins. But it hydro- 

 lyses the proteoses and peptones and also casein. The 

 final products of action are the same as in the case of 

 trypsin, that is, free amino-acids. But it would seem that 

 it can break down many of the polypeptides that are 

 resistant to the action of trypsin. Thus the products of 

 ereptic digestion may fail to give the biuret reaction, 

 whereas the most prolonged tryptic digests give a vivid 

 reaction owing to the polypeptides present. The enzyme 

 is probably of great importance in protein digestion in 

 completing the hydrolysis initiated by the successive action 

 of pepsin and trypsin. It is usually stated that the 

 optimum P H for the action of erepsin is 7-8. 



Preparation. Obtain a length of the small intestine of a recently killed 

 pig. Wash out the contents under the tap, split open, and spread on a board 

 with the mucous membrane uppermost. Scrape this off the muscle coats with 

 the back of a scalpel, placing the material in a weighed dish. Determine the 

 weight of mucosa obtained. Grind it with sand, add about 15 times its weight 

 of water and transfer to a flask. Add some toluol and shake. After standing 

 for about half an hour add i gram, of sodium chloride for every 100 cc. of water 

 taken, shake till dissolved, and filter through a pleated paper. Filtration is 

 very slow, and may take several hours. It can be accelerated by the addition 

 of a little acetic acid, which precipitates some of the mucin and nucleo-proteins 

 which make the solution so slimy. There is a risk of destroying the enzymes 

 by adding too much acid, but in some cases the addition of minimal amounts 



