CELLULAR DIFFERENTIATION AND INTERNAL 



ENVIRONMENT^ 



By ROSS G. HARRISON 



OSBORN ZOOLOGICAL LABORATORY, YALE UNIVERSITY, NEW HAVEN, CONN., 

 AND NATIONAL RESEARCH COUNCIL, WASHINGTON, D. C. 



It may not be inappropriate in begin- 

 ning this discussion to refer to a passage 

 from Psalm 139, which seems to be ger- 

 mane to the subject. 



14. I will praise Thee; for I am fearfully and 

 wonderfully made : marvelous are Thy works ; 

 and that my soul knoweth right well. 



15. My substance was not hid from Thee, when 

 I was made in secret, and curiously wrought 

 in the lowest parts of the earth. 



16. Thine eyes did see my substance, yet being 

 unperf ect ; and in Thy book all my members 

 were written, which in continuance were 

 fashioned, when as yet there was none of 

 them. 



There are several remarkable things 

 about this text. First, it refers to de- 

 velopment as a personal experience; and, 

 indeed, all of us have been through it. 

 This in itself should arouse our curiosity, 

 but unfortunately we have no recollection 

 of the adventure. It is also to be noted 

 that the process of development is de- 

 scribed here as a sort of epigenesis. ''And 

 in Thy book all my members were written, 

 which in continuance were fashioned, when 

 as yet there was none of them." It does 

 not picture development, in the naive 

 manner, as a mere unfolding or ^'evolu- 

 tio" of something already present. 



While this symposium deals with the cell 

 in all of its aspects, the topic assigned to 

 me, "Cellular Differentiation and Internal 

 Environment," clearly concerns the de- 

 velopment of the organism and implies that 

 the treatment of the subject should be in 

 terms of the cell as a unit. With this I 

 am wholly in agreement, for in my opinion 

 none of the attacks that have been made 

 upon the cell theory have shaken it to any 

 appreciable degree. 



1 The lecture was illustrated by numerous lan- 

 tern slides. 



It seems to be a characteristic of the 

 human mind to describe the phenomena of 

 nature in terms of units or particles. 

 Physics, chemistry, and crystallography 

 have all profited immensely by this device, 

 even though modern physics tells us that 

 nature cannot be fully described in such 

 terms alone. Such theories are oversim- 

 plifications and are sooner or later modi- 

 fied; witness the atomic theory of the 19th 

 century. But it may be doubted if science 

 can advance without the aid of over-simpli- 

 fied hypotheses. 



The cell theory differs from other par- 

 ticulate theories in the circumstance that 

 the units can actually be seen under the 

 microscope and sometimes even by the 

 naked eye. Each unit is composed of two 

 main constituents — nucleus and cytoplasm. 

 However, the fact of individual visibilitj^ 

 does not mean that there are no difficulties 

 or uncertainties connected with the theory. 



One of the notions that has frequently 

 aroused opposition is the concept of the 

 organism as a cell state made up of quasi- 

 independent or autonomous units, the cells. 

 The inadequacy of this concept was empha- 

 sized by Conklin, who declared that there 

 is something in the organization of the 

 individual that makes it more than the sum 

 of its parts. While this statement in itself 

 may be unobjectionable, the mystical haze 

 that often surrounds the word "organiza- 

 tion" has no place in science. 



I doubt if there is any astute and serious 

 observer who thinks of particulate units at 

 any level as wholly independent of one 

 another. The relations of the particles are 

 part of the system, and it is their behavior 

 in relation to one another that constitutes 

 ' ' organization. ' ' These relations are amen- 

 able to experimental investigation and are 

 usually expressed in some kind of a con- 



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