78 INORGANIC INGREDIENTS. 



\ not free. 

 Silicon J 



lodin. 



Oxygen. 



Hydrogen. 



Nitrogen. 



Marsh-gas. 



Ammonia. 



Sulphuretted Hydrogen. 



Hydrochloric Acid. 



Carbon Dioxid. 



Water (H 2 O). Water is one of the most important of the 

 physiologic ingredients. Its quantity in the human body is vari- 

 ously stated by different authorities: Halliburton placing it at 

 58.5 per cent, of the body-weight of an adult, and 66.4 per cent. 

 of that of infants, while others give it as 68 per cent. It is found 

 in all the tissues, both solid and fluid. 



Quantity of Water in the Body. The percentage of water in 

 some of the solids and fluids of the body is as follows : 



Enamel of teeth ................... 0.2 



Dentin ....................... 10. 



Bones (undried) .................. 50. 



Costal cartilage ................... 67.66 



Corpuscles of venous blood .............. 68. 16 



Muscles ............. ......... 73. 



Human milk .................... 87. 



Plasma of venous blood ............... 90.15 



Urine ....................... 93. 



Gastric juice .................... 98. 



Perspiration .................... 98. 



Saliva ....................... 99. 



Pulmonary vapor .................. 99. 



From this table it will be seen that while water makes up but 

 a small part of the enamel of the teeth, it constitutes almost the 

 whole of the saliva. Between these two extremes it is present 

 in different tissues in varying proportions. It should be said of 

 these, and of most other quantities given in physiologic tables, 

 that they are not invariable, hence the analyses of different author- 

 ities will vary. The composition of the milk, for instance, is not 

 always the same ; therefore there will not invariably be 87 per 

 cent, of water present; but the normal variations from this figure, 

 either above or below, will not be very great, and the percentages 

 given in the above table may be regarded as averages. 



Offices of Water. We should naturally infer from the large 

 quantity of water present in the body, and from its universal 

 presence in all the solids and liquids, that its offices must be 

 important ; and a study of these demonstrates that this is a fact. 

 It is the water which gives to fluids their fluidity. Without this 

 property the blood could not circulate through the blood-vessels, 



