1 882.] Organic Compounds in their Relations to Life. 971 



hydrocarbon group from which it is wanting is quite distinct 

 from all others. Hydrogen comes next in point of regularity, 

 and these three elements make up the great bulk of all organic 

 matter. When nitrogen is added a marked change is made in the 

 nature of the compounds. The nitrogenous group is distinguished 

 especially by its great instability, and also by the number of 

 isomeric forms which these bodies are capable of assuming. The 

 only other elements that enter to any great extent into organic 

 compounds are sulphur and phosphorus. These occur in limited 

 but definite proportions in many of the most complex substances. 

 The remarkable contrasts which the elements of organic com- 

 pounds present when compared with one another have been fre- 

 quently pointed out by different writers, and they are certainly 

 \ adequate to explain most of the properties possessed by these 

 bodies. The chief characteristic of oxygen is its great chemical 

 activity, or tendency to combine with other substances, while 

 that of nitrogen is its inertia, or inability so to combine. Carbon 

 is a solid at all temperatures producible on the globe, while all the 

 other three chief constituents of organic matter are practically 

 incapable of solidification. This fact is a measure of the degree 

 of cohesion of the homogeneous molecules composing the respec- 

 tive molar aggregates; that of carbon is intense, while that of 

 hydrogen is exceedingly slight. While this in each case depends 

 on the degree of heat, it will be relatively the same among them 

 all at any given temperature. 



It would appear that all the attempts, so to speak, on the part 

 of nature to form compounds of the gaseous elements alone have 

 resulted, where successful, in substances which are at once pro- 

 nounced inorganic, such as water, H..O, ammonia NH 8 , nitric 

 acid, HNO.,, etc. It is remarkable that while the chief compound 

 of the two persistent gases, hydrogen and oxygen, is liquid 

 (water) or solid (ice) at our temperatures, that formed of the per- 

 sistent solid, carbon, in combination with one of these gases, 

 oxygen (carbonic dioxide, C0 2 ), is a gas at all ordinary tempera- 

 tures and pressures. Notwithstanding this, it can not be doubted 

 that carbon is the agent which, by its great molecular cohesion 

 prevents the dissolution of the higher compounds and renders 

 organic substances possible. 



As already remarked, the transition from the inorganic to the 

 organic is, from the point of view of chemical structure, purely 



