206 METAMORPHOSIS OF TISSUE. 



in the chemical molecules by the action of the vegetable cell, the 

 object of which is to separate the oxygen as far as possible, and to 

 restore the most complicated radicals (the most perfect organic 

 matter), whilst the animal organism borrows this matter from the 

 plant for the purpose of finding a main support for the most 

 important animal functions in the regressive motion which the 

 oxygen generates in the oxidisable matters. Hence it is true 

 that oxygen is the exciter of animal life ; through its agency the 

 primary mucus or the plasma becomes converted into a cell, the 

 cell is developed into fibre, and animal matter into the animal. 



Yet however much truth may attach itself to such abstract 

 assertions, we always find in association with the truth the germs 

 of many errors. In treating of the formation of organic matter in 

 the vegetable kingdom (p. 180), we noticed the concurrence of 

 several processes of oxidation with the deoxidation going on in the 

 plant ; in like manner we also find in the animal organism, in 

 addition to the oxidation in the blood of the capillaries, numerous 

 processes of reduction, scarcely less intense than those which we 

 meet with in plants ; thus, for instance, in the primse vise we have 

 seen that substances, such as sulphates, which require the most 

 powerful agents for their reduction, were completely deprived of 

 their oxygen (see vol. i, p. 445) ; that the oxides of iron and 

 mercury, and similar substances, were deoxidised in the intestine ; 

 whilst we elsewhere drew attention to the fact that the fats and 

 lipoids, which are first formed in the animal body, can only be 

 produced by a process of deoxidation. Even if we assume that 

 oleic and margaric acids are formed from starch or sugar by such 

 a process of cleavage as that by which alcohol is generated from 

 sugar, (so that the reduction is only an apparent one, since the body 

 is simply decomposed into one richer in oxygen, namely, carbonic 

 acid, and into one poorer in oxygen, as alcohol, fusel oil, margarin, 

 or olein) ; yet stearic acid, which is very rarely taken up by animals 

 in vegetable food (hitherto it has only been found in cacao-butter), 

 must be formed by a direct process of deoxidation, as both its com- 

 position and its chemical qualities show that it can only be regarded 

 as a lower stage of the oxidation of the radical of margaric acid ? 

 Nor can we assume that a substance so poor in oxygen as cholesterin, 

 which so readily accumulates in the stagnant fluids of the animal 

 body, can be formed from the simple decomposition of some organic 

 matter. The oxidising force of the animal organism is bounded 

 by tolerably narrow limits ; sulphide of potassium, when present in 

 sufficient quantities, passes, in part, in an unoxidised form into the 



