152 Notes, ii. I. 



A. (Z>. G. et C. ii. 8, l), some proportion of every one of the four elementary substances. 

 The differences between substances depended therefore not on differences in the elements, 

 of which they were made, but on differences in the ever-varying proportions in which 

 these were combined to form them. 



A. distinguished clearly enough between chemical combination and mere mixture. 

 In the former, he says (Z>. G. et C. i. 10), the combining substances disappear with their 

 properties, and a new substance with new properties arises from their unification. In 

 the latter the mixed substances remain with all their properties, and it is merely the 

 imperfection of our vision which prevents us from seeing the particles of each lying side 

 by side and separate. Had we the eyes of Lynceus we should do so, however intimate 

 the mixture might be. But though A. thus distinguished chemical combination from 

 mechanical mixture, he had no notion of preferential aflSnities, nor of course of com- 

 bination in definite proportions. The elementary bodies combined with each other with 

 perfect indifference, and in any chance proportions. There was thus no such thing as 

 definite composition, and consequently no such thing as definite properties in substances. 

 One piece of matter might resemble another more or less, but that it should be identical 

 with it in composition and therefore in properties was, in the infinity of possibilities, so 

 improbable as to be out of the question. 



The compound substances then are formed by combinations of the four elementary 

 substances, and this is A.'s first degree of composition ; the study of which has developed, 

 as Frantzius remarks, into modern Chemistry. From these compounds the homogeneous 

 parts or tissues are formed. This is the second degree of composition, and its study 

 corresponds to our Histology. Lastly from the tissues are formed the heterogeneous parts 

 or organs, which are dealt with by Descriptive Anatomy. It is strange that A. should * 

 not allude here to the higher grade of composition, namely the formation of the 

 whole body from the organs. Presumably he omits it, as being a stage not reached by 

 all organisms. Cf. ii. I, Note 8. 



5. The division of the parts into Homogeneous and Heterogeneous, which A. puts 

 forward so prominently in this book, corresponds to the more modern division into Tissues 

 and Organs ; the main difference being that A. includes among his homogeneous parts 

 not only the tissues but even the secretions. It was the revival of A.'s doctrine in a 

 more perfect form that first made the name of Bichat illustrious. 



The heterogeneous parts or organs are formed from the homogeneous parts or tissues. 

 From what are the tissues formed? A. said, directly from the compound substances. 

 Modern histologists as a rule say from cells, fibres and the like, which they interpose 

 between the tissue and its constituent chemical substances. A. knew of nothing answering 

 to these "morphological units," the tissue being to him the last term in the structural 

 analysis. In fact before the microscope was invented the existence of the cell could not 

 be suspected. Theophrastus however, the pupil of A., seems to have tried to resolve the 

 tissue into simpler elements, though still more complex ones than its physical or, as we 

 should now say, its chemical constituents. "Other parts there are," he says, speaking 

 of the organs of plants, "from which these are formed, such as bark, pith, wood, all of 

 which are homogeneous. There are parts again anterior even to these, and from which 

 these are made. Such are juice, fibre, vessel, flesh. These are the primary constituents ; 

 there being nothing anterior to them, unless one reckons in the elementary properties of 

 matter, which are the common basis of all substances " {HUt. Plant, i. 2). 



6. The fact that, with similar material to select from, man generates man and plant 

 plant, shows that it is not the material that determines the process, but the process that 

 determines the material. 



