676 Journal of Agriculture. [10 Nov., 1908. 



standing, it becomes alkaline in reaction, phosphates are thrown out of 

 solution as cloudy precipitates. The urine of the herbivores on the other 

 hand is alkaline and turbid. The solid matter held in suspension consists 

 chiefly of carbonates of lime and magnesia so that the urine effervesces on 

 adding acid. Oxalate of lime is also present in the form of minute 

 crystals. Phosphates are present in very small quantities, these substances 

 in' herbivores being excreted mainly by the bowel. Potassium is generally 

 in excess of sodium. Hippuric acid and aromatic bodies, including 

 carbolic acid and pyrocatechin, are present in appreciable quantities. The 

 urine of herbivores when placed in a glass vessel will be found to darken 

 from the surface downwards just as a photographic developer will do; :n 

 fact some aromatic bodies present in herbivore urine can actually be used 

 for developing photographs ! The relatively large quantities of oxalic 

 acid and aromatic bodies are due to the presence of these substances pre- 

 formed in the food ; thus a horse fed on meadow-hay will excrete three 

 times as much hippuric acid as one fed chiefly on oats. 



It is interesting to note that, when a herbivorous animal is allowed to 

 starve, its urine becomes similar to that of a carnivore. This is due to the 

 fact that the starving animal lives on its own tissues and is therefore in all 

 truth a carnivore. 



The number of waste products and of foreign substances, inert or 

 poisonous, that appear in the urine is very large and no useful purpose 

 could be served by attempting to name them here. Not a }ear passes but 

 some new ingredient of urine is discovered ; but the substances named above 

 constitute by far the greater portion of the solid matter present. 



The following table gives an idea of the composition of human urine 

 taking this as a type : — 



Quantity in 24 hours ... ... ... 1,500 ccs.* 



Urea ... ... ... ... ... .30.0 prms. 



Uric acid ... ... ... ... 0-7 ,, 



Kreatinin ... ... ... ... 1"0 ,, 



Hippuric acid ... ... ... ... 0'7 ,, 



< )tlier organic matter ... ... 2*6 ,, 



Total organic matter ... ... ... 35.0 ,, 



Sodium chloride ... ... ... 15.0 ,, 



Pho.sphoric acid ... ... ... 2'5 ,, 



Potassium .. ... ... ... 3".3 ,, 



Other mineral matter ... ... ... 4"2 ,, 



Total mineral matter ... ... ... 25.0 ,, 



Total solids ... ... ... ... (iO.O ,, 



Tn the healthy animal neither blood nor haemoglobin should be present 

 in the urine. If such appear it means disease or accident, or poisoning by 

 such substances as pine-needles, fox-glove, spurge, &c. Sugar in health 

 is present only in the minutest traces. Albumen is absent, though in most 

 mammals the unrine may contain some slimy mucin or nucleo-protein 

 derived from the urinary tracts — bladder and urethra chieflv. Bile appears 

 in the urine in certain diseases such as jaundice. 



XV.— The Afferent Systems. 



In Chapter III. it was stated that all nerve impulses entering the ner- 

 vous system start in definite end-organs or receptors which are specially at- 

 tuned to some particular form of stimulus. A brief list was also given of 

 the chief types of receptors. These we must now examine in greater 



* 1,000 fc. — 1 litre. ] grain ^ l.i-J uraiii';. 



