ORGANIC STRUCTURE: MORPHOLOGICAL 53 



became part of the notion of the animal mechanism in addition 

 to structure in the old-fashioned, mechanical sense. 



Chemical structure. Later still chemical ideas were made. The 

 muscles, nerves, bones, glands, circulating fluids, etc., had definite 

 chemical structure. When the parts of the mechanism (now a 

 physical- chemical one) were actuated the eff"ects that followed 

 depended on the chemical structure as well as on the ways in 

 which the visible parts of the machine were placed in relation to 

 each other. Perhaps the idea of a machine as stated above may 

 hold valid with regard to chemical systems : the properties of 

 the latter depend on the ways in which the atoms of chemical 

 compounds are placed in relation to each other. 



Microscopical structure. Study of gross structure did not carry 

 the early physiologists very far : Thus Galenic physiology 

 supposed that blood passed through pores in the septum between 

 the right and left ventricles of the heart, although these pores 

 could not be seen : they were parts of an assumed invisible 

 structure. Later, of course, study of morphological structure, 

 assisted by the microscope, showed that the pores did not exist 

 but that blood passed from right to left sides of the heart by means 

 of previously invisible vessels — the capillaries. 



So in the early part of the nineteenth century much was expected 

 to be learned as to organic functioning by the study of micro- 

 scopic structure. 



Ultra-microscopic structure. Even now much of our notions 

 of functioning is based on structure that is ultra-microscopic but 

 still assumed to exist. Thus there are viruses that are supposed 

 to be structural entities but which are beyond the range of the 

 microscope. So are the genes of the mendelians (see Section 81^). 

 Like the Galenic ventricular pores, these are assumed in explana- 

 tions. 



Chemical structure is, of course, ultra-microscopic. Such 

 constitutional formulae as are quoted in Section 8 can hardly 

 be regarded as other than convenient symbols that are most 

 useful in explaining (or rather, describing) chemical reactions. 

 Enzymes are only quasi-chemical entities and even a symbolism, 

 such as that used to describe proteins, cannot be framed to describe 

 their structure (if they have definite chemical individuality in 

 the sense that the proteins have such). 



Cellular structure and functioning. And in the last resort the 



