148 ON THE PRODUCTION OF INFUSORIA. 



i 



It does not differ from digestion, excepting- that the term is never used 

 when the temperature of the mass is raised beyond that of the sur- 

 rounding air. 



On the nature and phenomenon of the putrefactive process in vege- 

 table matter, we have the following excellent account in Rees's 

 Cyclopaedia : — 



" The conditions necessary for the putrefaction of vegetables are 

 similar to those required in the putrefaction of animal substances. It 

 is necessary that the organisation be impregnated with water; the contact 

 of air is necessary, as also a certain degree of heat ; and for the due 

 effect of this kind of decomposition, the* vegetables should be heaped 

 together, and their juices be abundant. In these circumstances, the 

 phenomena of decomposition are as follow : — the colour of the vegetable 

 is changed, the green leaves become yellow, the texture becomes lax, 

 the parts less coherent, the colour of the vegetable itself changes to 

 black or brown, the mass rises and perceptibly swells up, the heat 

 becomes more intense, and is perceived on approaching the heap ; and 

 the fumes that arise have already a smell, which sometimes is not dis- 

 agreeable ; at the same time bubbles arise and break at the surface of 

 the liquid, when the vegetables are reduced to a magma, or mass of 

 feculent matter. This gas is a mixture of nitrogen, hydrogen, and 

 carbonic acid. At this epocha, likewise, an ammoniacal gas is emitted, 

 which is formed in these circumstances ; and in proportion as these 

 appearances diminish, the strong and offensive odour is succeeded by 

 another which is fainter and milder, and the mass becomes dry. The 

 internal part still exhibits the vegetable structure when the stem is 

 solid, and the fibrous matter has been the predominating principle ; and 

 it then constitutes manure or soil. Hence it arises that the herbaceous 

 plants of a loose texture, and abounding in juices, are not capable of 

 forming manure by their decomposition, but are reduced to a brown 

 mass of little consistence, in which neither fibre nor texture is observed; 

 and this is what for the most part forms vegetable mould." 



This is, decidedly, one of the clearest descriptions that can possibly 

 be given of the theory and phenomena of vegetable putrefaction. The 

 circumstances, however, are not the same as those recorded by " Tyro ;" 

 and, consequently, the effects, or results, or products will be different. 

 Let us then examine each. 



First, in the usual circumstances there are the following conditions : 

 1, impregnation (not maceration) with water; 2, the contact of air ; 

 3, the accumulation of the vegetable matter in a heap. 



