57 



found in the arterial blood. Chyle, lymph and blood are simply to 

 be regarded as the means by which the transportation is effected of the 

 decomposable and decomposed material ; the decomposition or change 

 itself is effected in the tissues. The various substances dissolved or 

 suspended in the arterial blood, such as albuminoids, fat, sugar, salts 

 and oxygen diffuse themselves through the fine capillaries of the blood 

 vessels into the fluids of the tissues and here it is that they are sub- 

 jected to all sorts of changes and transformations. The products of 

 these are gathered up into the dark venous blood, which carries them 

 away to be discharged from the body, while another set of fine tubes, 

 the lymphatic absorbents, pick up all healthy superfluous fluid from the 

 various tissues and return it into the circulation. 



The albuminous substances thus spread all over the system are 

 split up into more and more simply organised bodies, the final products 

 being urea and uric acid. Just how this transformation 



is effected is far from being clearly understood. But there is not the 

 slightest doubt about the fact tnat the substance urea, which 

 contains nearly 50 per cent, of nitrogen, together with small quantities 

 of uric acid and ammonia, is the ultimate product of the decomposition 

 of the albuminoids in the animal organism, and is completely removed 

 from the body by the instrumentality of the kidneys. Consequently 

 the quantity of urea produced in the animal body furnishes a measure 

 of the quantities of albuminoids consumed. The nitrogen of 100 parts 

 of albuminoids is capable of producing 33.45 parts of urea and if the 

 constituents of the latter are substracted from the albuminoids thus : 



C. H. N. O. 



In 100 pts albuminoids .... 53-53 7.06 15-61 23.80 

 In 33.45 urea 6.69 2.23 15-61 8.92 



There remain. . .. 46.84 4.83 .... 14.88 



which are applied either direct to sustain the animal heat or are 

 deposited in the body as fat. Thus, while the carbon, to a very large 

 extent, of the albuminoids in common with that of the carbo-hydrates 

 either promotes the production of fat or finds its way in the shape of 

 carbonic acid to the lungs, and is so discharged into the atmosphere, a 

 very different fate is experienced by the nitrogen. In some mysterious 



