PRACTICAL PHYSIOLOGY. 



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smelt (odour of burned feathers), and the latter black from the 

 formation of lead sulphide. 



(b.) Heat some dry proteid with excess of soda-hme in a hard 

 dry tube ; ammonia vapour is evolved. 



(c.) Place a few grains of the dry proteid, with a 

 small piece of metallic sodium, in a dry hard tube, 

 and heat slowly at first, and then strongly. After 

 cooling, add carefully 3 cc. of water to the NaCy 

 residue, filter, and to the filtrate add a few drops of 

 ferric chloride and ferrous sulphate, and then add 

 excess of hydrochloric acid. If nitrogen be present, 

 there is a precipitate of Berlin blue, sometimes only 

 seen after standing for a time. 



{d. ) To a solution of albumin add an equal volume 

 of solution of caustic potash and a few drops of lead 

 acetate and boil for some time = slowly a brownish 

 colouration, due to lead sulphide. 



3. Determination of Temperature of Coagulation 



(fig. i). — The reaction of the fluid must be neutral 

 or feebly acid. **A glass beaker containing water 

 is placed within a second larger beaker also contain- 

 ing water, the two being separated by a ring of cork. 

 Into the water contained in the inner beaker there 

 is immersed a test-tube, in which is fixed an accurately 

 graduated thermometer, provided with a long narrow 

 bulb. The solution of the proteid, of which the 

 temperature of coagulation is to be determined, is 

 placed in the test-tube, the quantity being just 

 sufficient to cover the thermometer bulb. The whole 

 Fig. I.— Apparatus for De- apparatus is then gradually heated, and the experi- 

 termining the Coagula- menter notes the temperature at which the liquid first 

 ^''o'leid?'"'' ' shows signs of opalescence » {Gamgee). 



4. Circumstances Modifying the Coagulating Temperature. — Place 5 cc. 

 of the solution of albumin in each of three test-tubes, colour them with a 

 neutral solution of litmus, and label them A, B, C. To A add a drop of very 

 dilute acetic acid (o. i per cent, acetic acid diluted five or six times); to B 

 add a very dilute solution of caustic soda (o. i per cent, of soda or potash 

 similarly diluted); C is neutral for comparison. Place all three tubes in a 

 beaker with water and heat them gradually, noting that coagulation occurs 

 first in A, next in C, and not at all in B, the alkaline solution. 



CLASSIFICATION OF PROTEIDS. 



5. I. Native Albumins are soluble in tcater, in dilute saline 

 solutions, in saturated solutions of sodic chloride, and magnesium 

 sulphate, and are not precipitated by alkaline carbonates, sodic 

 chloride, or very dilute acids. They are precipitated by saturating 

 their solutions with ammonium sulphate. These solutions are 

 coagulated by heat at 70° to 73° C, although the temperature 



