322 LYMPH AND LYMPHATIC GLANDS [CH. XXII. 



Loeb and his fellow-workers have confirmed these statements, but interpret 

 them now as ionic action. Contractile tissues will not contract in pure solutions of 

 non-electrolytes (like sugar, urea, albumin). But different contractile tissues differ 

 in the nature of the ions which are most favourable stimuli. Thus cardiac muscle, 

 cilia, amoeboid movement, karyokinesis, cell division, are all alike in requiring a 

 proper adjustment of ions in their surroundings 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 con- 

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

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

 that is, they accelerate the action of Na, though they do not themselves 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 contrac- 

 tions 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, etc.) 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 spermatozoon 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. So also must the equally important idea that the basis of a nerve- 

 impulse is electrolytic action. 



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 sub- 

 stance per litre. Thus a gramme-molecular solution of sodium chloride is one which 

 contains 58'5 grammes of sodium chloride (Na = 23'05: Cl = 35'45) in a litre. A 

 gramme-molecular solution of grape sugar (C 6 H 12 O 6 ) is one which contains 179 '58 

 grammes of grape sugar in a litre. A gramme-molecule of hydrogen (H 2 ) 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 179*58 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 upon 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, and the 

 process is called diffusion. In a similar way diffusion will effect in time a homo- 

 geneous mixture of two liquids or solutions. If water is carefully poured on to the 

 surface of a solution of salt, the salt or its ions will soon be equally distributed 

 throughout the whole. If a solution of albumin or any other colloidal substance is 

 used instead of salt in the experiment, diffusion will be found to occur much more 

 slowly. If, instead of pouring the water on to the surface of a solution of salt or 

 sugar, the two are separated by a membrane made of such a material as parchment 

 paper, a similar diffusion will occur, though more slowly than in cases where the 

 membrane is absent. In time, the water on each side of the membrane will contain 

 the same quantity of sugar or salt. Substances which pass through such membranes 

 are called crystalloids. Substances which have such large molecules (starch, pro- 



