Journal of Agricidiurc. [8 Feb., 190^ 



The following table giyes the percentage amount by weight of water in 

 a number of tissues : — 



Per cent. Per cent. 



Enamel of tooth ... 0.2 Cartilage ... ... 54 — 74 



Dentine of tooth ... 10 Muscles, glands, blood, 



Fatty tissue ... 6 — 12 and brain... ... 75 — 80 



Bone ... ... 14 — 40 



The percentage amount of water in the bodv as a whole is subject to 

 continual variation ; young animals have always a higher percentage than 

 adults, and lean animals than fat. It is, however, safe to state that, on an 

 average, tAvo-thircis, or 66 per cent., of the weight of the animal bod} is 

 water. 



Metallic Compounds. 



Chlorides, carbonates and phosphates of .sodium, potassium, magnesium, 

 and calcium are found in animal bodies, and are absolutely essential to 

 life.* It is a very suggestive fact that these salts are present in blood in 

 much the same relative proportions as they occur in sea water. In fact, a 

 mixture of one part sea water and three parts pure water, if pumped 

 through the vessels of an organ (for instance, the heart or bowel) which 

 has been removed from a living or recently killed animal, will maintain 

 life in that organ for many hours. A somewhat diluted mixture can keep 

 the heart of a tortoise alive and beating vigorously for some days. On the 

 other hand, we find that an.y disturbance of the ejuantities of these salts in 

 the blood (as regards either the total amount present or their mutual ratios), 

 if not promptly rectified by the kidneys, will bring about serious derange- 

 ments of every living cell in the body. As sodium chloride, or common 

 salt, is the chief salt of the blood, we find animals instinctively endeavour- 

 ing to keep up the supply ; but too much of this substance will be injurious 

 as well as too little, as is seen in the case of castaways Avho' drink sea water. 

 An animal fed exclusively on maize grains will soon be afflicted with 

 muscular weakness and other troubles indicatiye of calcium staryation ; the 

 same often follows from exclusive oatmeal feeding. 



How far these actions of salts are due to their combination with the 

 nitrogenous ingredients of bioplasm, and how far to their electrical state, 

 we do not at present know. This, however, is certain, that their presence 

 in a fixed quantity and proportion is an absolute essential of life. 



Another metallic compound which, unlike the foregoing, can hardly be 

 called a metallic salt is the compound of iron which exists in the blood, and 

 to which blood owes its red colour. Iron is so widely distributed in nature 

 that a deficient supply in food must be of rare occurrence; it is, however, 

 often stated that an adult mammal liying exclusiyely on a milk diet suffers 

 from iron starvation. 



When the bodv of an animal or a portion of such is subjected to heat 

 strong enough to burn all the carbon compounds present, the metallic com- 

 pounds are left behind, and form what is called the ash. The composition 

 of the ash varies with the portion of the body thus tested ; for instance, 

 bone ash is chiefly calcium phosphate, mu.scle ash is chiefly potassium 

 phosphate, and blood ash is chieflv sodium chloride. The percentage 

 amount of ash in the whole body will vary with different species of animals, 

 and will vary even with individuals of the same species. Generally speaking 



^Sulphates are also found to a slight extent in the blood, but they are probably 

 waste products Avhich the kidney is always endeavouring to remove. 



