I 



ADDKESS. 21 



injury is not repaired by the production of fresh specimens of their 

 characteristic cells, as would be the case in injuries to bones and tendons. 



In our endeavours to differentiate the function of the nucleus from 

 that of the cell plasm, we should not regard the former as concerned 

 only in the production of young cells, and the latter as the exclusive 

 agent in growth, nutrition, and, where gland cells are concerned, in the 

 formation of their characteristic products. As regards cell reproduction 

 also, though the process of division begins in the nucleus in its chromo- 

 some constituents, the achromatic figure in the cell plasm undoubtedly 

 plays a part, and the cell plasm itself ultimately undergoes cleavage. 



A few years ago the tendency amongst biologists was to ignore or 

 attach but little importance to the physiological use of the nucleus in the 

 nucleated cell, and to regard the protoplasm as the essential and active 

 constituent of living matter ; so much so, indeed, was this the case that 

 independent organisms regarded as distinct species were described as con- 

 sisting of protoplasm destitute of a nucleus ; also that scraps of proto- 

 plasm separated from larger nucleated masses could, when isolated, exhibit 

 vital phenomena. There is reason to believe that a fragment of protoplasm, 

 when isolated from the nucleus of a cell, though retaining its contractility 

 and capable of nourishing itself for a short time, cannot increase in amount, 

 act as a secreting structure, or reproduce its kind : it soon loses its 

 activity, withers, and dies. In order that these qualities of living matter 

 should be retained, a nucleus is by most observers regarded as necessary 

 (Nussbaum, Gruber, Haberlandt, Korschelt), and that for the complete 

 manifestation of vital activity both nucleus and cell plasm are required. 



Bacteria. 



The observations of Cohn, made about thirty years ago, and those of 

 De Bary shortly afterwards, brought into notice a group of organisms to 

 which the name ' bacterium ' or ' microbe ' is given. They were seen to vary 

 in shape : some were rounded specks called cocci, others were straight rods 

 called bacilli, others were curved or spiral rods, vibrios or spirillse. All were 

 chai-acterised by their extreme minuteness, and required for their exami- 

 nation the highest powers of the best microscopes. Many bacteria 

 measure in their least diameter not more than ij^s-J-iroth of an inch, 

 i\yth the diameter of a human white blood corpuscle. Through the re- 

 searches of Pasteur, Lord Lister, Koch, and other observers, bacteria have 

 been shown to play an important part in nature. They exercise a very re- 

 markable power over organic substances, especially those which are com- 

 plex in chemical constitution, and can resolve them into simpler combina- 

 tions. Owing to this property, some bacteria are of great economic value, 

 and without their agency many of our industries could not be pursued ; 

 others again, and these are the most talked of, exercise a malign influ- 

 ence in the production of the most deadly diseases which afflict man and 

 the domestic animals. 



