804 



SCIENCE 



[N. S. Vol. XXXVI. No. 937 



to advantage be placed. We will ask, not 

 ' ' what is an organism, ' ' but what is organ- 

 ization? The first question is too compre- 

 hensive and therefore vague and unwork- 

 able. The latter question, aiming at the 

 very essence of what we want to know, 

 enables us to turn from the distracting 

 complexity of the entire organism to any 

 observable part of it, the smaller and 

 simpler the better, which exhibits that dis- 

 tinctive characteristic of the whole, organ- 

 ization. 



A familiar form of anatomical descrip- 

 tion begins by stating that the morpholog- 

 ical unit is the cell. Cells, then, are asso- 

 ciated together to form tissues, which enter 

 into the composition of organs. Several 

 organs cooperating in a set of related func- 

 tions constitute an organ-system. The 

 whole animal, finally, may consist of sev- 

 eral such organ-systems. A complete de- 

 scription of structure would lead us to a 

 considerably greater degree of complexity, 

 for we should find units intermediate be- 

 tween certain of those which we have just 

 mentioned. Thus, the kidney as a whole 

 we call an organ. But analysis resolves it, 

 not immediately into tissues, but first into 

 such secondary or lesser organs as renal 

 tubules, renal corpuscles and blood-vessels. 



Turning from the morphological to the 

 physiological point of view, we observe a 

 series of units of function precisely cor- 

 responding to the series of structural units. 

 It could not be otherwise, for structure is 

 merely the visible expression of function. 



Whether we view the structural or the 

 functional aspect of the animal, we see the 

 component units so correlated and coor- 

 dinated one with another that the result is 

 a harmonious action of the whole in rela- 

 tion to a fairly well-defined set of external 

 conditions. This systematizing of many 

 lesser units into one greater unit is so 



striking a peculiarity of living things that 

 we call them organisms. 



Organization, however, is a peculiarity 

 not merely of the animal or plant as a 

 whole, but likewise, to a considerable de- 

 gree of minuteness, of its constituent struc- 

 tural units. There are certain things 

 which cells do quite independently of the 

 fact that they belong to any particular 

 tissue or animal. The fundamental proc- 

 esses of metabolism, growth and reproduc- 

 tion are inherent in cells. Obviously, a 

 tissue cell has an organization within itself. 

 So far as my present purpose is concerned, 

 it would not now be profitable to speculate 

 as to how far there may be still other self- 

 contained organizations within and inferior 

 to the cell. A tissue, likewise, has a cer- 

 tain organization within itself. There are 

 certain activities which a tissue performs 

 quite independently of the fact that it is a 

 part of a particular organ or animal. 

 Muscle tissue, removed under appropriate 

 experimental conditions from the animal to 

 which it belongs, exhibits its characteristic 

 activities. The contraction of an excised 

 piece of muscle is, to be sure, merely the 

 resultant of the contractions of its con- 

 stituent cells. I speak of it as a tissue act 

 rather than a cell act in the sense that it is 

 action of a specialized type — one not ex- 

 hibited by cells in general but only by such 

 cells as possess those peculiarities charac- 

 teristic of muscle tissue. A small bit of 

 epithelium transplanted into a foreign lo- 

 cality, or maintained under artificial cul- 

 tural conditions, may exhibit its peculiar 

 habits of growth. The essential fimction 

 of an epidermis is to cover outside surface. 

 If a portion of an animal is denuded of 

 epidermis, the remaining epidermis, pro- 

 vided the wound is not too extensive, ex- 

 tends over and covers the exposed deeper 

 tissues. If a small fragment of living ani- 



