532 THE AIH AND LIFE. 



tliey are aided in reacliiug the roots by means of sprinkling with water 

 in which rich eartli has been kept for a few hours, the plant will at 

 once prosper. Better still, if two leguminous plants are put in sterilized 

 soil, and if, as was done by M. Breal of the Museum, a small quantity 

 of the liquid, charged with microbes that fills the nodes of any thriving 

 legumincms plant, be injected into the root of one of the two plants, 

 it nourishes at once, whilst the other that was not inoculated remains 

 stunted. There is no controverting this demonstration. The microbes 

 on the roots of leguminous i)lants are agents through which plants 

 assimilate nitrogen. A new study is open to agricultnrists and there 

 is no doubt that other facts of tlie same purport will be discovered 

 in this unsuspected field of investigation. In our present discussion 

 we need only know that atmospheric nitrogen is retained by plants, 

 and, as we know that nitrogenous food is necessary to higher beings, 

 and that the sni)ply of such food can invariably be traced back to jjlants, 

 we may conclude that the nitrogen of air is an indisi)ensable agent in 

 animal as well as vegetable life. Though an inert, and at first glance 

 useless gas, it nevertheless performs an essential function in nutrition 

 of all beings. Our legitimate conclusion therefore is that without nitro- 

 gen there can be no food, no plants, no life. It is proper to add that 

 plants derive nitrogen not exclusively from air, iV)r nitrates and ammo- 

 nia also sui)ply some, but these compounds are themselves drawn from 

 atmospheric nitrogen and our proposition remains true. 



We now come to carbonic acid. That gas, as we know, is in the 

 highest degree a noxious element, and without doubt we shall find 

 nothing but mischief to charge to its account. It is indeed noxious, 

 and we lose no time in expelling it from our organism; it is irrespira- 

 ble, and plants as well as animals soon die when placed in a medium 

 containing even a comparatively slight ])ropt)rtion of it. Even 1 per 

 cent of carbonic acid in air causes perceptible disorders to life, and 

 when there is 10 per cent life is in danger, and death is l)ut a question 

 of time. The tissues are injured by blood charged with carbonic acid, 

 and when we breathe au atmos])here rich with this gas the blood glob- 

 ules only imperfectly discharge the carbonic acid that they gathered 

 from the tissues, and on returning to these tissues the blood is there- 

 fore charged with that gas and lacks oxygen, or, in other words, is 

 quite unfit to sui)port life. The reason Avhy these blood globules retain 

 the carbonic acid when coming in contact with impure atmosphere is 

 that they are unable to throw it off unless its tension in the atmosj^here 

 be less than in the globules. Now, when that gas is superabundant 

 in the atmosphere, its tension is greater there than in the globules, 

 and, in the absence of any cause inciting separation from the globules, 

 the gas is retained and suffocates the animal by killing its tissues. 

 Before producing death there is a decided anaesthesia which Bichat 

 fully proved by experiments, in which he injected into the carotid 

 and nervous centers of an animal, venous blood charged with carbonic 



