202 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



stimuli. Thus cardiac muscle, cilia, amoeboid movement, karyokinesis, cell 

 division are all alike in requiring a proper adjustment of ions in their sur- 

 roundings if they are to continue to act, but the proportions must be different 

 in individual cases. Ions affecting the rhythmical contractions may be 

 divided into three classes : (1) Those which produce such contractions ; of 

 these the most efficacious is Na. (2) Those which retard or inhibit 

 rhythmical contractions ; for instance, Ca and K. (3) Those which act cata- 

 lytically, that is, they accelerate the action of Na, though they do not them- 

 selves produce rhythmical contractions directly : for instance, H and OH. 

 In spite of the antagonistic effect of Ca, a certain minimal amount of it must 

 be present if contractions are to continue for any length of time. Ions produce 

 rhythmical contraction only because they affect either the physical condition 

 of the colloidal substances (proteid &c.) in protoplasm, or the rapidity of 

 chemical processes. 



Loeb has even gone so far as to consider that the process of fertilisation is 

 mainly ionic action. He denies that the nuclein in the head of the sperma- 

 tozoon is essential, but asserts that all the spermatozoon does is to act as the 

 stimulus in the due adjustment of the proportions of the surrounding ions. 

 He supports this view by numerous experiments on ova, in which, without the 

 presence of spermatozoa, he has produced larvae (generally imperfect ones, 

 it is true) by merely altering the saline constituents of the fluid that bathes 

 them. Whether such a sweeping and almost revolutionary notion will stand 

 the test of further verification must be left to the future. 



Gramme-molecular Solutions. — From the point of view of osmotic pressure 

 a convenient unit is the gramme -molecule. A gramme-molecule of any 

 substance is the quantity in grammes of that substance equal to its molecular 

 weight. A gramme-molecular solution is one which contains a gramme- 

 molecule of the substance per htre. Thus a gramme-molecular solution of 

 sodium chloride is one which contains 58'5 grammes of sodium chloride 

 (Na = 23"05 ; CI = 35"45) in a litre. A gramme-molecular solution of grape 

 sugar (CgHijO,;) is one which contains 180 grammes of grape sugar in a 

 litre. A gramme-molecule of hydrogen (H^) is 2 grammes by weight of 

 hydrogen, and if this was compressed to the volume of a litre, it would be 

 comparable to a gramme -molecular solution. It therefore follows that a 

 litre containing 2 grammes of hydrogen contains the same number of 

 molecules of hydrogen in it as a litre of "a solution containing 58-5 grammes 

 of sodium chloride, or one containing 180 grammes of grape sugar, has in 

 it of salt or sugar molecules respectively. To put it another way, the heavier 

 the weight of a molecule of any substance the more of that substance must 

 be dissolved in the litre to obtain its gramme-molecular solution. Or still 

 another way : if solutions of various substances are made all of the same 

 strength per cent., the solutions of the materials of small molecular weight 

 will contain more molecules of those materials than the solutions of the 

 materials which have heavy molecules. We shall see that the calculation of 

 osmotic pressure depends \ipon these facts. 



Diffusion, Dialysis, Osmosis. — If two gases are brought together within a 

 closed space, a homogeneous mixture of the two is soon obtained. This is 

 due to the movements of the gaseous molecules within the confining space, 



