AIR AND LIFE. 167 



beings are adapted to their environment, and that the adaptation is 

 often very strict. He has shown that oxygen — the vivifying gas par 

 excellence, that which is essential to life — is also a violent poison; a 

 poison for plants as well as for animals, for the cells and the whole 

 organism. All that is required is for oxygen to acquire a certain ten- 

 sion in the atmosphere or — what amounts to the same — be present in 

 a certain ratio above the normal, and it becomes an agent of death. 

 This can be demonstrated in two ways. Animals or plants may be 

 made to live in a normal atmosphere, but under higher pressure than 

 the average; or, again, they may be placed in artificial air where the 

 ratio of oxygen has been increased. In both cases the phenomena are 

 similar; in both, death is the result. While a satisfactory explanation 

 has not yet been proposed in the case of plants, Paul Bert has been 

 able to show that animals die in a superoxygenated atmosphere as 

 soon as their blood contains one-third more than the normal ratio of 

 oxygen, because, in such an atmosphere, the hemoglobin of the red 

 blood corpuscles is saturated with' oxygen — a fact which never occurs 

 under normal conditions — and a proportion of this gas then dissolves 

 in the serum of the blood itself. The oxygen dissolved in the serum 

 does all the harm. The tissues can not withstand the presence of free 

 uncombined oxygen; they are killed. This is the quo modo of the 

 phenomenon. The quare is yet wanting: Why do the tigsues require 

 combined oxygen, and why does free oxygen kjll them? Here is a 

 riddle for physiologists; it is one worth their pains and trouble. 



Now, it must be said that while a certain increase in the ratio of 

 oxygen results in death, lesser increases of a temporary character may 

 be beneficial. Every poison kills, doubtless, but there are doses which 

 not only do not kill, but even confer benefit and improve health. This 

 toxicity of superabundant oxygen is undoubtedly one of the most 

 curious facts that recent years have brought to light, and it is a very 

 positive and demonstrable one. 



On the other hand, to say that without free oxygen there can be no life 

 would be incorrect. Pasteur's investigations have shown that if some 

 micro-organisms can live only where air and oxygen are present, others, 

 which have been termed anaerobic, much prefer an environment where 

 air is wanting. Such is the case with those which cause fermentation. 

 They induce fermentation only when in a medium devoid of oxygen, 

 and, as Pasteur put it, fermentation is a consequence of life without 

 air. What then occurs in a fermenting medium? A particular kind 

 of microbe — each fermentation is due to a particular sort or species of 

 microbe — is conveyed, by air, by water, or is purposely introduced, into 

 that medium. During a time it lives there upon the oxygen which it 

 finds. At last oxygen fails; all the provision has been expended, and 

 diffusion lias not taken place rapidly enough to meet the needs of the 

 micro-organism. The latter has then to shift for itself in some manner. 

 Free oxygen is wanting, to be sure, but nevertheless there is oxygen 



