HISTORICAL SKETCH 435 



by making artificial emulsions with soaps and oils which showed amoeboid 

 movement and other striking resemblances to living protoplasm. 



The modern studies discussed in Chapter II have placed a new evalua- 

 tion on these early structural theories. What their proponents saw was 

 not the fundamental structure of protoplasm but secondary structural 

 modifications and differentiation products. Thus Biitschli's alveoles 

 were innumerable minute masses of various vacuolar and other sub- 

 stances. Any distinction between large vacuoles, alveoles, and ultra- 

 microscopic colloidal masses of the same material is more or less arbitrary, 

 though the physico-chemical properties of the system may be expected to 

 vary with the degree of subdivision. It is now evident that it is mainly 

 in the hyaline "ground substance" that fundamental structure is to be 

 sought, and that the appearances observed by the above pioneers do not 

 have the significance originally attributed to them. 



It would be difficult to overestimate the value, both practical and 

 theoretical, of the protoplasm doctrine, for its establishment has not only 

 led to knowledge by which the conditions of life have been materially 

 improved but has also been an important factor in assisting man to a 

 modern, rational outlook on organic nature. It is not too much to say 

 that the identification of protoplasm as the material substratum of the 

 life processes was one of the most significant events of the nineteenth 

 century. The doctrine was furnished with a popular expression by Hux- 

 ley in his well-known essay, The Physical Basis of Life (1868). 



The Organismal Theory. — The conception of the cell had by this 

 time developed into something quite different from what it had been in 

 the minds of the founders of the cell theory. The cell was now recognized 

 as a protoplasmic unit, and the ideas of these men concerning the origin 

 of cells had been overthrown. Future researches were to show more 

 clearly the role of cells in connection with development and inheritance, 

 and certain limits were to be set to the conception of the cell as a unit of 

 function and organization. To Dutrochet and Schwann the multi- 

 cellular plant or animal appeared as little more than a cell aggregate, the 

 cells being the primary individualities; the organism was looked upon as 

 something completely dependent upon their varied activities for all its 

 phenomena. "The cause of nutrition and growth," said Schwann, 

 "resides not in the organism as a whole, but in the separate elementary 

 parts — the cells." This elementalistic conception of the organism as an 

 aggregate of independent vital units governing the activities of the whole 

 dominated biology for many years, nowithstanding its severe criticism 

 by Sachs, de Bary, and many other later writers who pointed out that, 

 owing to the high degree of physiological differentiation among the various 

 tissues and organs, the cell cannot be regarded merely as an independent 

 unit but as an integral part of a higher individual organization, and that 



