ON PHYSIOLOGICAL MORPHOLOGY. 47 



of sodium chloride, in 100 cubic centimetres of sea-water, are 

 represented on the axis of the abscissa, the values for the 

 increase in growth on the ordinate axis. 



These and similar experiments, which on account of lack of 

 time I cannot mention here, show that growth in animals is de- 

 termined by the same mechanical forces that determine growth 

 in plants. An obstacle to such a conclusion seems to lie in 

 the fact that many plant cells have solid walls, while such is 

 not the case in most animal cells. But the solid cell-wall does 

 not determine the peculiar character of growth. This charac- 

 ter is determined first, by chemical processes within the cell, 

 which result in a higher osmotic pressure, and, secondly, by 

 the osmotic qualities of the outer layer of protoplasm, which 

 allows water to pass through freely, but does not allow all salts 

 dissolved in it to do the same. Both these qualities are inde- 

 pendent of the solid cell-wall, and I see no reason why the 

 animal cell should not agree in these two salient features with 

 the plant cell. 



In order that the foregoing explanation of the mechanism of 

 growth in the animal cell might be based only upon known 

 processes, it was necessary to find out whether, indeed, in case 

 of growth, chemical processes of such a character take place 

 that there are formed substances of higher osmotic pressure 

 than those from which they originate. Every one knows that 

 by practice our muscles increase in size. No satisfactory 

 explanation of this fact has been given. If my interpretation 

 of the method of growth was correct, I must expect that during 

 activity there are formed in the muscle substances which deter- 

 mine a higher osmotic pressure than those from which they 

 originate. This is exactly the case. Ranke had already shown 

 that the blood of a tetanized frog loses water and that this 

 water is taken up by the muscles. In experiments which were 

 carried on by Miss E. Cooke in my laboratory, we were able to 

 show directly that during activity the osmotic pressure inside 

 the cell-wall is raised. We determined the concentration of a 

 solution of Na Cl, or rather of a so-called Ringers mixture, in 

 which the gastroconemius of a frog neither lost nor took up 

 water. We found that while this concentration for the resting 



