186 CIRCULATING FLUIDS : 



favorable circumstances, a portion of tlie sugar will crystal- 

 lize. In consequence of its intimate mixture with a large 

 quantity of extractive matter, an exact quantitative analysis of 

 the sugar is extremely difficult. The best method is that 

 of fermentation, and estimating the quantity of carbonic acid 

 that is formed. If the quantity of sugar be very minute, it 

 cannot be recognized by the tongue, in consequence of the 

 sweetness being disguised by the taste of the salts and extractive 

 matter ; it may, however, in this case, be detected by sulphuric 

 acid, although this test is fallacious in the hands of unpractised 

 analysts. The method to be pursued in this case is the same 

 as that previously indicated; the spirituous solution must be 

 evaporated, treated with anhydrous alcohol, and the fluid de- 

 canted. The precipitate which contains extractive matter, 

 chloride of sodium, lactate of soda, and sugar, must be dissolved 

 in water ; and if (as is frequently the case) any htematoglobulin 

 remains undissolved, the fluid must be filtered. The filtered 

 fluid must be evaporated to drjTiess in a porcelain basin, on the 

 water-bath, and one or two drops of dilute sulphuric acid (one 

 part of acid to six of water) must be dropped upon the dried 

 residue. On again submitting it to the heat of the water-bath, 

 it is observed that those points which have been moistened by 

 the acid at first assume a blue or violet tint, become gradually 

 darker, and ultimately coal-black. When the quantity of sugar 

 is very small, the colour is only sufficiently marked at the margin 

 of the drop, or at points where the layer of extractive matter 

 happens to be particularly thick. Unfortunately for the suc- 

 cess of this test, a dark spot, varying from a deep brown to a 

 dark dirty-violet tinge, but never positively black, is produced 

 in the same manner in the spirit- extract of blood, which con- 

 tains no sugar; so that, without a av ell-practised eye, it is 

 difficult to decide upon the absence or presence of sugar by this 

 test. After the addition of one grain of diabetic sugar in 

 solution, to 500 grains of blood, (which contained no sugar,) no 

 decided sweetness could be observed in the spirit-extract. The 

 sulphuric acid test indicated the presence of sugar by the for- 

 mation of a coal-black spot ; on the addition of the acid to a 

 portion of the extract of the same blood in which there was no 

 sugar, a dirty \dolet spot was produced. In examining the 

 blood of diabetic patients I once found so large a proportion of 



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