286 NON-NITROGENOUS NEUTRAL BODIES. 



betic urine, be not very active after the addition of yeast, we must 

 not draw any conclusions regarding the presence of sugar, for yeast 

 promotes the decomposition of the animal fluids a process which 

 is often accompanied with the development of a little gas. If, 

 however, no yeast be added to the urine, but we wait for spon- 

 taneous fermentation, as has also been recommended, the de- 

 velopment of carbonic acid proceeds very slowly, unless an ex- 

 tremely large quantity of sugar be present; moreover, in this 

 case, there is this additional difficulty in observing the 

 formation of the gas, that the sugar for the most part undergoes 

 the lactic and not the vinous fermentation. As the detection 

 of the alcohol, which is formed during this process, is by no 

 means easy, attention has been drawn to the formation of the 

 yeast-fungus (Torula cerevisice) as a characteristic indication of 

 vinous fermentation. For those who are accustomed to the use of 

 the microscope, and are well acquainted with the appearance of 

 the Torula^ this is unquestionably an easy and certain test ; but it 

 must be borne in mind, that when normal urine has been allowed 

 to stand for a long time, especially at a high temperature, fungi 

 of a precisely similar shape are formed in it, probably, for the most 

 part, from the mucus. These fungi, which are by no means 

 dependent on the decomposition of sugar, may exist in urine still 

 preserving a decidedly acid reaction, although they more frequently 

 occur in neutral urine ; the individual cells, which, like the yeast- 

 cells, (Torula cerevisice,) contain distinct nuclei, are mostly about 

 one-half (in diameter) smaller than the true yeast-cells ; but inde- 

 pendently of the circumstance that under the microscope apparent 

 magnitudes afford a very relative criterion, the yeast-cells which 

 are first and spontaneously formed, are always much smaller than 

 those which are subsequently produced by gemmation from pre- 

 viously formed yeast-fungi. 



A very good means of discovering sugar, and of determining- 

 its quantity with considerable accuracy in a clear solution, isaffordea 

 by Biot and Soleil's polarising apparatus; its expense will, how- 

 ever, always stand in the way of its general application. 



We have already shown (p. 124) that Pettenkofer's test is not 

 available for the detection of sugar. 



All other tests which were formerly employed for the discovery 

 of sugar (evaporation with hydrochloric or sulphuric acid, treat- 

 ment with chromic acid, boiling with caustic potash, &c.) are open 

 to so many sources of fallacy, as compared with the methods we 

 have already indicated, that we may pass them over in silence. 



