50 THE MECHANISM OF LIFE 



haemoglobin approximately in a "6 per cent, solution. A 

 solution of "9 per cent, of NaCl is therefore isotonic to the 

 contents of the red blood corpuscles, to the serum of the blood, 

 and to the cells of the tissues. It by no means follows that 

 the cells of the blood and tissues undergo no change when 

 irrigated with a 9 per cent, solution of chloride of sodium. 

 They do not lose or gain water, it is true, and they retain 

 their volume and their specific gravity. But they do undergo 

 a chemical alteration, by the exchange of their electrolytes 

 with those of the solution. Hamburger has pointed out that 

 in mammals the shape of the red corpuscles is altered in every 

 liquid other than the blood serum ; even in the lymph of the 

 same animal there is a diminution of the long diameter, and 

 an increase of the shorter diameter, while the concave discs 

 become more spherical. 



All the cells of a living organism are extremely sensitive to 

 slight differences of osmotic pressure — the cells of epithelial 

 tissue and of the nervous system as well as the blood cells. For 

 instance, the introduction of too concentrated a saline solution 

 into the nasal cavity will set up rhinitis and destroy the 

 terminations of the olfactory nerves. Pure water, on the other 

 hand, is itself a caustic. There is a spring at Gastein, in the 

 Tyrol, which is called the poison spring, the " Gift-Brunnen.'" 

 The water of this spring is almost absolutely pure, hence it 

 has a tendency to distend and burst the epithelium cells of the 

 digestive tract, and thus gives rise to the deleterious effects 

 which have given it its name. Ordinary drinking water is 

 never pure, it contains in solution salts from the soil and gi^c^ 

 from the atmosphere. These give it an osmotic pressure 

 which prevents the deleterious effects of a strongly hypotonic 

 liquid. During a surgical operation it is of the first importance 

 not to injure the living surfaces by flooding them with 

 strongly hypertonic or hypotonic solutions. This precaution 

 becomes still more important when foreign liquids are brought 

 into contact with the delicate cells of the large surfaces of the 

 serous membranes. Gardeners are well aware of the noxious 

 influence of a low osmotic pressure. They water the soil 

 around the roots of a plant, so that the water may take up 



