Chap, v.] CONSTITUTION OF ORGANISED BODIES. 41 



accepted by M. C. Robin — it would be necessary to class among 

 the constituent elements the globules suspended in the blood, 

 the haemaiia, which yet are evidently elements produced, and of 

 brief duration. 



From the point of view of ultimate physical constitution, of 

 the mode of molecular collocation, we must consider every living 

 element as being formed by a blending, molecule by molecule, 

 of immediate principles, belonging to the three classes already 

 indicated. All these immediate principles are dissolved in one of 

 them, in water, which in weight is by far the most important 

 body. In effect, living elements need a certain minimum of con- 

 stituent water without which they can neither get nutriment nor 

 as a result perform their functions. 



In the vegetal elements, as Sachs remarks,^ we can prove 

 this intimate blending of the immediate principles, by extracting 

 from those elements, by the aid of certain solvents, substances 

 chemically determined, without thereby changing the form of 

 the histological skeleton. 



There exists between the anatomical vegetal elements and the 

 animal elements an important difference in the degree of chemi- 

 cal stability. The animal elements are much more easily alter- 

 able by physical and chemical agents. In plants there is a 

 certain degree of mineral fixity manifestly in relation with 

 their smaller degree of vital perfection and activity. MM. 

 Naegeli and Schwendener, studying carefully the play of pola- 

 rised light in the vegetal cellular membranes, the particles of 

 starch, and also in the vegetal crystalloidal bodies, have found 

 that in these vegetal tissues and elements there must be crystal- 

 lised molecules birefringent and with double optical axes. These 

 facts are perfectly in accordance with the difference of chemical 

 composition of tissues in the two organised kingdoms. "We shall 

 see in effect that the most characteristic chemical element of 

 organised substances, azote, enters in relatively feeble propor- 

 tion into the compositi(m^f plants. Now the presence of azote 

 1 J. Sachs, Traitide Botanique, p. 768. Paris, 1874. 



