IMBIBITION. 37 



consider protoplasm. Of all organised bodies protoplasm is 

 the one which most nearly approaches a fluid, as is shewn by 

 the fact that it tends to assume a spherical form when in a 

 state of equilibrium. But it is, nevertheless, not a fluid ; it is 

 a semi-fluid. We may define such a body, as Pfaundler has 

 done, by saying that it consists of an intermixture of groups 

 of solid and of fluid molecules. Assuming Strasburger's 

 theory of the molecular structure of organised bodies, we 

 must regard the molecular structure of protoplasm as capable 

 of undergoing constant modification, the grouping of the 

 molecules being in a state of perpetual change, the result 

 of this molecular activity being the phenomena which we 

 term vital, and which distinguish protoplasm, as living, from 

 all other organised bodies. 



II. The swelling-up of Organised Bodies (Imbibition). 



We have already become familiar with this "phenomenon, 

 and we have discussed in detail the explanations of it which 

 have been offered. We will now briefly consider its broader 

 features which are independent of any theory as to the actual 

 mode in which it is effected. 



The force with which water is thus absorbed is very con- 

 siderable ; it is not only sufficiently great to overcome the 

 elastic resistance which is offered by the molecules of the body 

 itself, but it can overcome a great external pressure in addi- 

 tion. This is well shewn by an experiment of Hales. He 

 filled an iron pot nearly full with peas and water, and placed 

 on the peas a leaden cover bearing a weight of 184 Ibs.; as 

 the peas began to swell, they raised the cover and the weight. 



The absorption of water by an organised body has been 

 found to be accompanied by an evolution of heat. This fact 

 appears to have been first definitely stated by Pouillet, but it 

 has since been observed by many investigators. Naegeli 

 found, for instance, that when 40 grmes. of perfectly dry 

 wheat-starch were mixed with an equal weight of water, the 

 temperature rose from 22 C. to 32*5 C. This evolution of heat 

 indicates that the absorption of water is accompanied by con- 



