THE ORGANISM. 13 



Structure of the Animal Body. 



The Organs and the Organism. 



§ 11. 



In the living' tody we observe a number of activities of its 

 material substratum^ by wliicli tbe series of pbasnomena spoken of as 

 life are conditioned. Underlying these, there are cliemico-physical 

 processes, which are accompanied by a continual degradation of the 

 material, and consequent metastasis, or change in the arrangement 

 of chemical elements. The body nourishes itself by replacing the 

 material used up in metastasis by fresh matter, which is received 

 from without; and this it assimilates, or makes like to the substances 

 of which it is itself composed. The substances, partly taken in with 

 the nutrient matter, partly produced by metastasis, which are of no 

 further use in the organism, are passed out. Hence results the 

 excretory function, if the quantity of matter assimilated is greater 

 than that which is expelled, there is an increase in the size of the 

 body: it grows. Thus it fulfils the first condition for the production 

 of that material from which a new organism, like to itself, arises : 

 and so reproduction is closely connected with nutrition. 



The body is, in the first place, in relation to the exterior by its 

 surface ; this puts it in connection with the surrounding medium. 

 Changes in the form of the surface of the body result in movements, 

 and give rise to locomotion. The surface also is the medium by 

 which it perceives the outer world, or has sensations. 



The parts of the body which preside over these processes are the 

 instruments by which life is carried on — organs. In virtue of 

 their existence the body is an organism, and when we also include 

 under the term " organisms " certain bodies in which no organs can 

 be individually separated, it is because the virtual existence of 

 organs in them is to be assumed from the mere fact that life is 

 carried on in them. The term " organism " is therefore employed 

 in this instance, not in an anatomical, but iu a physiological sense. 

 In the simplest condition of the organism, the vital phtenomena 

 take place in the homogeneous substance which forms the body, 

 and which is the seat of all these processes equally. The body 



