36 



in the proteids, and is commonly called peptonization. The 

 peptonization, or digestion, of milk is quite often practised 

 in the preparation of food for the sick room, and is illustrated 

 by the following experiment. Dilute about lo cc. of milk 

 with an equal volume of distilled water and add a half a 

 gram of sodium bicarbonate. Then add a few drops of 

 pancreatic extract, shake the mixture and keep at 40° C. on 

 the water-bath for about a half an hour. Then filter and 

 apply the biuret test for peptones. The pancreatic extract 

 from beef acts more strongly upon the proteids ; that from 

 the pig is very active in converting starch into sugar. 



159. Place a small quantity of milk in a warm place for 

 one or two days ; then test the reaction, it will be found to 

 be acid ; this is due to ferTnentation , in the process of which 

 the milk sugar is converted into lactic acid. 



XIV. 



160. An examination of some of the more important 

 tissues of the body. 



161. Saline extract of Nervous Tissue. The solids of a 

 saline extract of the brain are derived chiefly from the gray 

 matter, (cinerea). 



162. Apply the xanthoproteic test to a portion of the 

 above extract. 



163. Faintly acidify another portion with acetic acid and 

 boil. If coagulated a proteid is present. This may be a 

 native albumin or globulin or both. 



164. An ethereal extract of the brain contains solids 

 derived chiefly from the white matter (alba). 



165. Pour out a little ethereal extract of brain upon paper 

 and note that there is a permanent greasy stain, indicating 

 the presence of fat. Remember that this is not wholly 

 ordinary fat, but largely a nitrogenous, phosphorated fat — 

 lecithin. 



