

THE PROTEIN SUBSTANCES. 8 1 



however, remain with the serum and may be separated by allowing the 

 latter to stand in a tall, narrow jar, or, better, by rotating the serum in 

 a centrifugal machine. Most of the corpuscles may be deposited in this 

 way, leaving a yellowish liquid. A pure white serum can not be obtained 

 because a little of the hemoglobin dissolves from the corpuscles and re- 

 mains in solution. With this prepared serum make the following tests: 



Ex. To a little of the serum add finely powdered magnesium sulphate to 

 saturation; this produces a precipitation of serum globulin, which sepa- 

 rates on standing. Pour off the clear liquid and add to it powdered 

 ammonium sulphate, which gives now a precipitate of albumin. 



Ex. Mix a little of the serum with two or three volumes of water in 

 a test-tube, and test the temperature of coagulation. It will be found 

 near 70 C. 



LACT ALBUMIN. Milk contains two protein substances, the 

 most important of which is casein. The other is a true albu- 

 min which is present to the extent of about one-half per cent 

 in cow's milk. It resembles serum albumin very closely but 

 appears to have a much lower specific rotation, [a]^ = 38. 



EGG ALBUMIN. White of egg contains this body as its 

 characteristic constituent along with some globulin and mucoid, 

 and traces of salts. Common albumin reactions are usually 

 made with white of egg solution. Although this substance is 

 ahvays described as a true albumin, some of its reactions seem 

 lo suggest that it may belong to the group of glucoproteids, 

 or, at any rate, may contain such a compound in relatively 

 large amount. On heating egg albumin with weak acid glucos- 

 amine is split off and in quantity sufficient to indicate a rather 

 large sugar content in the original substance. The specific 

 rotation is much lower than that of serum albumin and may 

 be taken at 



which is about the value for milk albumin. Besides this dif- 

 ference, egg albumin has a much lower coagulating tempera- 

 ture than has been given for serum albumin, viz., 56. Egg 

 albumin is much more easily coagulated by ether than is serum 

 albumin. Egg albumin becomes very quickly insoluble when 

 mixed with strong alcohol. From serum albumin it differs, 

 further, by this interesting property. When its solution is 

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