THE BIOLOGY OF THE CELL SURFACE 



of granules has been demonstrated, which respond to 

 reagents as does chromatin (a substance found in nuclei). 

 In others, by means of tests with dyes, chemical reagents, 

 etc., investigators have demonstrated areas which respond 

 as do nuclei in larger cells. Such systems are said to 

 possess diffuse nuclei. 



So much is clear: there are living forms which show no 

 discrete nuclei. This fact indicates that in the organiza- 

 tion of protoplasm the presence of a discrete nucleus is not 

 indispensable. 



The blue-green algae — bacteria are very closely related 

 to them — evoke special interest because they probably 

 represent the first forms of plant-life that arose on the earth. 

 If it be established that there exist non-nucleated blue-green 

 algae, this might mean that in the emergence of life, nucleus 

 and cytoplasm were undifferentiated and only subsequently 

 in the course of evolution became separated. 



Doubtless there exists living matter of such minute size 

 that it can not be seen with the highest powers of the 

 microscope. Whether or not such protoplasmic systems 

 possess the organization exhibited by cells seen under the 

 microscope remains to be learned. In a discussion of the 

 visible form of organisms it would be futile to include 

 invisible forms. Nor can ultra-filterable viruses be 

 included. In addition to the fact that they are of submicro- 

 scopic size is the question whether they be living things or 

 only the product of living things. If they be living, they 

 may despite their minute size possess thenucleo-cytoplasmic 

 organization of visible cells; or, lacking such they may 

 prove to be the most elementary protoplasmic system — ■ 

 protoplasmic ground-substance without clearly differen- 

 tiated regions. 



Many organisms consist of a mass of cytoplasm contain- 

 ing two or more nuclei. These may be low forms of life. 

 Protozoa, like the slime-mould or the multi-nucleated 



32 



