2'2 REACTION OF URINE. 



of which is small, and is filled with mercury; the other, a larger 

 one, is filled with air; from the large one there arises a gradu- 

 ated stem. The weight of the instrument is such that, when 

 placed in distilled water at 60 Fahr., it sinks to such an ex- 

 tent that the water is precisely on a level with the first divi- 

 sion of the graduated scale. The instrument, following the 

 law, that solids of a given weight sink deeper in the light 

 than heavy fluids, when introduced into any ordinary sample 

 of urine, sinks, so that the fluid is on a level with one of the 

 divisions of the scale. The instrument is so adjusted that 

 the division indicates the density or specific gravity of the 

 sample of urine examined. Thus if the fluid be on a level 

 with division 30 of the urinometer, we conclude that its den- 

 sity is 1030. 



The reaction of urine in disease next claims our attention. 



It has already been stated that the urine of the herbivpra is 



normally alkaline, that that of the carnivora is normally acid. 



In disease, however, the conditions are sometimes reversed, 



^and it is of importance that the practitioner should know 



^ 'how to ascertain this alkaline urine, like all other alkaline 



^fluids, changes the yellow colour of turmeric paper (paper 



e-dipped in an infusion of turmeric) to brown, and does not 



affect the blue colour of litmus paper, but restores the blue 



colour when the paper has been reddened by acids. On the 



other hand, acid urine changes the colour of blue litmus 



paper to red, and does not turn yellow turmeric paper brown. 



There are other reactions which enable us to detect whether 



a fluid, such as the urine, be alkaline or acid, but those 



already described suffice for all practical purposes. 



It has already been stated that the urine of the herbivora 

 is normally alkaline, but that, in disease, it sometimes 

 becomes acid; that the urine of the carnivora is acid, but 

 that, under the use of particular diet, it may become 



