28 



PRACTICAL PHYSIOLOGY. 



[III. 



was filled with distilled water i.e., zero = is the rotation due to the 

 dextrose = a. 



(/.) Place 10 cc. of the solution of dextrose in a weighed capsule, evaporate 

 to dryness over a water-bath, let the capsule cool in a desiccator, and weigh 

 again. The increase in weight gives the amount of dextrose in 10 cc. ; so that 

 the amount in i cc. is got at once = p. 



(g. ) Calculate the specific rotatory power by the above formula. It is about 



+ 53. 



For practice, begin with a solution of dextrose containing 1 1 grams per 100 cc. 

 of water. Make several readings of the amount of rotation, and take the mean. 



Example. In this case, the mean of the readings was 11.6. 



^ii.6 



.11X2 



= 53 



Repeat the process with a 4 and 2 per cent, solution. It is necessary to be 

 able to read to two minutes, but considerable practice is required to enable one 

 to detect when the two halves of the field have exactly the same intensity. 



Test the rotatory power of corresponding solutions of cane-sugar, arid any 

 other sugar you please. 



Test also the rotatory power of a proteid solution. 



The following indicate the S. R. for yellow light : 



Proteids. Egg-albumin - 35.5 ; serum-albumin - 56 ; syntonin 

 -72; alkali-albumin prepared from serum-albumin - 86, when 

 prepared from egg-albumin - 47. 



Carbohydrates. Glucose + 56 ; maltose + 1 50 ; lactose -f 52.5. 



N.B. A complication sometimes arises in connection with carbohydrates, 

 as the S.R. is sometimes much altered by the temperature ; thus the S.R. of 

 laevulose, when heated from 20-90 C. , falls in the pro- 

 portion of 3 : 2. It is best, therefore, to work at a 

 constant temperature, say 20 C. Again, some solutions 

 have not the same S.R. when they are first dissolved 

 that they have twenty-four hours afterwards. This is 



a ^^^^M called birotation, and it is therefore well to use the 

 solution twenty-four hours after it is made. 



Wild's Polari trobometer. Between the 

 polariser (which can be rotated) and analyser 

 of this instrument is placed a Savart's polari- 

 scope, which produces in the field a number of 

 parallel dark interference-lines. 



A framework H, which can be moved on a brass 

 support F, carries the analyser and polariser. The 

 light from a soda-flame enters at D, traverses a Mcol's 

 prism which is fixed to and moves with the graduated 

 index K. The polarised rays then traverse the fluid 

 contained in a tube placed in L, and reach the fixed 

 ocular parts containing the so-called polariscope. The 

 latter is composed of two prisms, which give rise to the interference-lines, which 

 are viewed by means of a lens of short focus. Between M and N is a diaphragm 

 with X -shaped cross lines. Beyond M, which is designed to protect the eye 



FlG. 14. a. Interference 

 lines seen with tig. 13. 



