ADDITIONS AND NOTES TO VOL. I. 467 



glucose and the other true sugars, but also with other carbo- 

 hydrates ; for on heating all such substances to 100, after the 

 application of chlorine or metallic chlorides, they are converted 

 into glistening black masses ; this happens not only with sugar, 

 but with woody fibre, hemp, linen, cotton, paper, starch, &c. 

 Hence it is easy to see that this method is open to many fallacies, 

 from the accidental presence of shreds of paper, dust, &c. If, 

 however, we had to deal with pure substances, we might certainly 

 recognise very small quantities of sugar, if, in accordance with 

 Maumene's directions, we moisten, with the fluid to be investi- 

 gated and then heat to 100 a pure woollen tissue (merino) 

 which had been previously saturated with a solution of chloride of 

 tin and afterwards dried. A glistening black patch is formed at the 

 spot that had been moistened. . 



(25) Addition to p. 287, 1 line from bottom. Moreover, this 

 method must be employed with considerable circumspection in 

 order to yield accurate results : for if the fluid which is being 

 examined contains other organic substances, which can either com- 

 bine with the alkali of the test-fluid, or can decompose oxide of 

 copper even to a slight degree, either the alcohol- extract of the 

 fluid, or the sugar-and-potash-compound, must be first exhibited 

 before the test can be applied. A second objection to this proce- 

 dure is, that we cannot keep the test-fluid for any length of time, 

 and that we, consequently, ought to prepare a fresh quantity for 

 each determination of sugar. In the course of time the alkali 

 exerts a modifying action on the tartaric acid, so as to give it the 

 property of reducing the oxide of copper with the co-operation 

 of heat, and, indeed, even in the cold. If we have boiled the freshly 

 prepared solution with the greatest care, and have convinced our- 

 selves that no suboxide is precipitated, we still find that after a 

 week a little of the suboxide is separated on boiling, and after it 

 has stood for a longer time, a similar decomposition ensues, even 

 at an ordinary temperature. This method is, however, by no 

 means to be rejected for this deficiency ; but at the same time we 

 must not overlook it. 



(26) Addition to p. 289, line 19. C. Schmidt* has subse- 

 quently shown that sugar is a normal constituent of the blood of 

 oxen, dogs, cats, and men ; and If have since found (almost simul- 



* Charakteristik der Cholera u. s. w. 1850, S. 161-168. 

 t Ber, d. Gesellsch. d. Wiss, zu Leipzig. 1850, Bd. 3, S. 139-141. 



2 H 2 



