2 INVERTEBRATE MORPHOLOGY. 



Dead protoplasm is somethiug very different from living pro- 

 toplasm, and our present knowledge only imperfectly extends 

 to this much-altered material. 



Furthermore even in the dead material the chemist has to 

 deal not only with the complex "substances which constitute 

 protoplasm proper, but also with numerous secondary prod- 

 ucts either in the process of being built up into protoplasmic 

 molecules or else resulting from the destruction of these 

 molecules. For both these processes are continually going 

 on, the living organism continually uniting simple chemical 

 compounds to form new complex molecules, a process known 

 as anabolism, and resulting in growth ; and just as continually 

 it is resolving into simpler compounds the complex mole- 

 cules already formed, a process known as catabolism, and 

 resulting in the manifestation of energy in its various forms, 

 such as h6at, motion, electricity, and even light. Growth and 

 the manifestation of energy are then two most important 

 phenomena exhibited by living organisms, standing in oppo- 

 sition to one another and determining the general condition 

 of the organism. If anabolic changes are the more active, 

 then the animal or plant grows, as we express it, adds new 

 protoplasm and increases in size ; if the anabolic and catabolic 

 changes are practically equal in amount, stability results ; 

 while the preponderance of catabolism leads to a lessening 

 of material, and finally to what we term death. These 

 changes constitute a cycle occurring in the life-history of 

 probably every organism and causing the periods which we 

 denote as youth, maturity, and old age. 



Dead protoplasm then, together with the anabolic and 

 catabolic constituents which are inextricably associated with 

 it, will be found on analysis to consist to a large extent of the 

 chemical elements Carbon, Hydrogen, Oxygen, and Nitrogen, 

 together with Sulphur and Phosphorus, as well as a number 

 of substances present in varying amounts, such as Chlorine, 

 Potassium, Sodium, Iron, Calcium, and Magnesium. Exactly 

 how these various elements are united together it is difficult 

 to determine, but especial importance has been assigned to 

 the C, H, O, N, and S compounds which occur and which form 

 a group of chemical compounds known as Proteids. Of such 



