MODERN BIOLOGY 595 



value of its results, competes well with experimental morphology and hered- 

 ity research. Unfortunately, these results are far less accessible for the pur- 

 poses of popular presentation than any other of the advanced spheres of 

 biology; in fact, biochemistry requires a very special technical training for 

 both its students and its critics. Nevertheless, space may be found here for 

 a few brief indications as to the most important progress that has been made 

 in its various special provinces in order to complete the picture of the gen- 

 eral progress made by experimental biology in modern times. 



That branch of chemical research which has had the greatest success 

 in our own day and has excited the keenest interest is undoubtedly physical 

 chemistry; each stage of its progress has at once been applicable to the liv- 

 ing substance. Biology has actually led the way in certain physico-chemical 

 discoveries, as in the question of osmotic pressure, in which the results of 

 Pfeffer's and de Vries's research-work formed the foundations on which 

 scientists have subsequently built further. On the other hand, the modern 

 theory of solutions, as created, among others, by van t'Hoff, Arrhenius, 

 and Nernst, has contributed towards explaining a great many biological 

 phenomena; as an instance may be mentioned the above-described partheno- 

 genetical phenomena in eggs that have been subjected to hypertonic saline 

 solutions; further may be quoted the part played by hydrogen ions in the 

 metabolism of the fluids of the body: they play a decisive part especially in 

 producing respiratory irritation, while other ion-combinations have been 

 found to be necessary for growth in individuals and organs. 



Colloid chemistry 

 Of special significance for forming a conception of the nature of protoplasm 

 has been modern colloid chemistry; it has founded a province of its own, 

 with its own methods, which have made it possible to study far more closely 

 than before the most minute structural details in the category of elements 

 in which living substance is included. Thanks to these accurate observations 

 and experiments, the granular and vacuolized structure of plasm has been 

 given a far more natural explanation than that once given by Biitschli in 

 his froth theory. It has in many instances been possible to compare the mu- 

 tual interpenetration of the various structures even with physico-chemical 

 metabolistic phenomena occurring in inanimate colloid substance, while, 

 on the other hand, the old dispute as to the solid or fluid nature of plasm 

 has lost all point; the intrinsic character of and changes in the colloids are 

 investigated on entirely different principles and have given rise to problems 

 utterly different from this old question of the state of aggregation. Instead, 

 extensive investigations have been made into the question of the penetra- 

 bility of cells and tissues by solutions of various kinds; in this sphere 

 especially Charles Ernest Overton (born in England in 1865, and after 

 studying in Germany appointed professor in Sweden) propounded a theory, 



