THIRD LECTURE. 



ON THE LIMITS OF DIVISIBILITY OF LIVING 



MATTER. 



JACQUES LOEB. 



I . If Physiology is to become a rational science in the same 

 sense in which Physics deserves this name, one of the funda- 

 mental problems to be solved is to determine how far the 

 divisibility of living matter goes, and what is the nature of its 

 ultimate elements. On the qualitative side of this question 

 attempts in that line were made simultaneously by Nussbaum 

 and Gruber. Nussbaum found that when he divided an infu- 

 sorian, only such pieces as contained nuclear substance were 

 able to regenerate the lost parts. " For the preservation of 

 an infusorian, it makes no difference how it is divided ; if only 

 the nuclear substance of the piece remains, it regains its orig- 

 inal form within twenty-four hours at the most, the length of 

 time required depending upon the temperature." "No growth 

 is possible in a piece which contains no nucleus. But such a 

 piece can retain its contractility — it can move." Among the 

 conclusions at which Nussbaum arrives, the following is of 

 most interest to us : " The cell is not the last physiological 

 unit, although it must remain such for the morphologist. We 

 are, however, not yet able to tell how far the divisibility of a 

 cell goes, and how we can determine the limit theoretically. 

 For the present it will be well not to apply to living matter 

 the notions atom and molecule, which are well defined in 

 Physics and Chemistry. The notion micella, introduced by 

 Nageli, will also lead to difficulties, as the properties of living 

 matter are based upon both nucleus and protoplasm." "The 

 cell always consists of an aggregate of individuals which are 

 similar one to another in Protozoa." In a very interesting 



