LABORATORY EXPERIMENTS 105 



from the lungs, skin, and kidneys, and, to a less extent, from the alimentary 

 ca.nal. The loss from these various organs may be thus apportioned (quoted 

 by Dalton from various observers) : 



From the alimentary canal (feces) 4 per cent. 



From the lungs 20 per cent. 



From the skin (perspiration) 30 per cent. 



From the kidneys (urine) 46 per cent. 



100 



LABORATORY EXPERIMENTS ON THE CHEMISTRY OF THE 



BODY. 



THE PROTEINS. 



i. Preparation of Proteins. The most convenient source of proteins 

 for laboratory work are blood serum, egg white, or commercial preparations 

 of the milk protein casein. Protein may also be prepared from various 

 plant seeds, especially cereals Hempseed contains a globulin, edestin, 

 which is very easily isolated in the laboratory. 



a. Preparation of Edestin. Grind up some hemp-seed in an ordinary 

 meat chopper and extract the resulting meal with 5 per cent, salt solution, 

 warming to 60. The solution should not be heated above 65 because 

 the protein will be coagulated. Filter while hot. On cooling slowly the 

 edestin will crystallize out. Examine some of the precipitate with a micro- 

 scope and sketch the crystals. The edestin is soluble in 10 per cent, salt 

 solution without warming, and solutions for laboratory use can be prepared 

 in this way. 



b. Preparation of Egg Albumin. The yolk should be separated from 

 the white of fresh eggs and the reticulum in the egg white broken up with 

 a wire egg-beater. Egg white can then be diluted as desired and the pre- 

 cipitate globulin filtered off. Crystals of ovalbumin can be prepared as 

 follows : 



The egg white, beaten as directed, is strained through gauze and an 

 equal volume of saturated ammonium sulphate solution is added. After 

 twenty-four hours the globulin precipitate is filtered off and concentrated 

 ammonium sulphate solution added until the mixture becomes turbid. 

 Then distilled water is added very carefully until turbidity has disappeared. 

 The solution is then acidified with acetic acid, which has been saturated 

 with ammonium sulphate, until a precipitate is obtained. The precipitate 

 is at first amorphous, and on standing becomes crystalline. Examine the 

 crystals under the microscope and sketch them. 



c. Other Protein Crystals. Crystals of hemoglobin may be demon- 

 strated by adding a drop of ether to diluted dog blood on the microscope 



