762 A MANUAL OF VETERINARY PHYSIOLOGY 



with phenyl-hydrazine, nor are they capable of undergoing alcoholic 

 fermentation. It is, in fact, a member of the benzene series, and 

 consists of a closed ring of six CH.OH groups. 



The sugars of chief physiological importance are the hexoses — 

 that is to say, a sugar such as dextrose which contains 6 atoms 

 of carbon in the molecule, or the disaccharides, which contain 12. 

 A series of artificial sugars have been produced containing 3 (trioses), 

 4, 5 (pentoses), 7, 8, and 9 atoms of carbon in their molecule. Of 

 these the pentoses alone at present possess any physiological interest. 

 This is due to the fact that a pentose may be obtained by the decom- 

 position of the nucleo-proteins of the pancreas and of yeast cells 

 These pentoses are not assimilable, as shown by their rapid appear- 

 ance in the urine after introduction into the body. Pentose yields 

 an osazone which melts at 160 C. 



Tests for Sugar — 1. Trommer's. — An excess of caustic potash and 

 a small amount of dilute solution of copper sulphate is added to 

 the fluid and the whole heated. The copper is reduced to suboxide 

 by the sugar, and a red precipitate falls. Fehling's solution, which 

 is used as a quantitative test for sugar, consists of hydrated cupric 

 oxide in caustic soda, and the double tartrate of sodium and potas- 

 sium. The principle of this test is the same — viz., the reclucing 

 action of the sugar, which robs the cupric compound of its oxygen. 



2. Moore's. — A solution of sugar boiled with caustic potash turns 

 brown. 



3. B ditcher's. — Bismuth oxide and excess of caustic potash are 

 added to the fluid containing sugar and heated. The solution be- 

 comes grey and then black, from the deposition of metallic bismuth. 



4. Picric Acid Test. — Boil the solution of sugar with a little picric 

 acid and caustic soda in small quantities ; a brown-red opaque 

 coloration is obtained. 



5. Fermentation Test. — The fluid containing a piece of yeast is 

 placed in a tube and inverted over mercury. If sugar is present it 

 undergoes fermentation, and carbonic acid is given off, which collects 

 in the tube. 



The osazone tests have already been described under the re- 

 spective sugars. They are very important to chemists for the 

 discrimination of the various sugars, as well as for their identifica- 

 tion. 



The Ferments. 



The conversion of one substance into another by the process of 

 fermentation must have acted as a stimulus in the search for the 

 philosopher's stone. To the ordinary mind, if sugar could be 

 converted into alcohol, why not lead into gold ? The extraordinary 

 phenomenon of a body being wholly changed into another, and bearing 

 not the faintest resemblance to its progenitor, is not only one of the 

 astonishing facts recorded by chemistry, but one of the wonders 

 of science. The nr.me ' fermentation ' was applied to the oldest 

 example of this phenomenon, and indicated a restlessness or agitation 

 in the fluid, the outcome of the generation of gas. When, later on, 

 this was shown to be due to the activity of micro-organisms, these 

 latter were naturally described as ferments. This term has remained, 

 though fermentation is now known not to be exclusively produced 

 by living organisms, but that non-living material may also excite 

 it. To these non-living ferments the distinguishing name of 

 enzymes is applied. 



