32 



NORMAL UlSTOLOCY. 



( Others consist in the cleavage of larger molecules into smaller atomic 

 groups which may variously unite with each other, chemical changes 

 designated as catabolic (catabolism). Similar cleavages may be 

 occasioned outside the body by various procedures employed in 

 chemical manipulations, but usually require powerful reagents in 

 concentration not met with in the body or the application of heat 

 greatly exceeding that compatible with life. It is believed, upon 

 experimental evidence, that these chemical changes within the cell 



Fig. 7. 



Schematic diagram of a cell: a, ectoplasm composed of hyaloplasm; b, spongioplasm ; c, 

 chromosome, composed of "chromatin," and forming a part of the intranuclear reticu- 

 lum ; between these chromatic fibres is the achromatin ; d, hyaloplasm in the meshes of 

 the spongioplasm ; e, one of the two nucleoli represented in the diagram ; /, one of eight 

 bodies constituting the metaplasm represented; g, centrosome, with radiate arrangement 

 hi' die surrounding spongioplasm ; //. nuclear membrane. 



are wrought with the aid of ferments or enzymes, chemical sub- 

 stance- produced by and present in the cell, which have the power 

 of facilitating chemical reactions and modifying the conditions under 

 which they take place, so that the plane upon which chemical equi- 

 librium is estal lished is shifted to a different level in the presence 

 cf ferments from that which it occupies when the enzymes are 

 absent, if one may be permitted to use such an illustration. A study 

 of such transformations constitutes a special field of chemistry, bio- 

 chemistry, in which great advances are being made. 



