September 14, 1900.] 



SCIENCE. 



389 



plasm, we should not regard tbe former as 

 concerned onlj' 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 under- 

 goes 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 consisting of protoplasm desti- 

 tute of a nucleus ; also that scraps of pro- 

 toplasm 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 re- 

 produce its kind : it soon loses its activity, 

 withers and dies. In order that these 

 qualities of living matter should be re- 

 tained, a nucleus is by most observers re- 

 garded as necessary (Nussbaum, Gruber, 

 Haberlandt, Korschelt), and for the com- 

 plete manifestations 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 ' bac- 

 terium ' 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 charac- 

 terized by their extreme minuteness, and 

 required for their examination the highest 

 powers of the best microscopes. Many bac- 

 teria measure in their least diameter not 

 more than 25000 ^^ ^^ ^^ inch, yV^^ tie di- 

 ameter of a human white blood corpuscle. 

 Through the researches of Pasteur, Lord 

 Lister, Koch, and other observers, bacteria 

 have been shown to play an important part 

 in nature. They exercise a very remark- 

 able power over organic siibstanees, especi- 

 ally those which are complex in chemical 

 constitution, and can resolve them into 

 simpler combinations. Owing to this prop- 

 erty, 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, ex- 

 ercise a malign influence in the production 

 of the most deadly diseases which afflict man 

 and the domestic animals. 



Great attention has been given to the 

 structure of bacteria and to their mode of 

 propagation. When examined in the living 

 state and magnified about 2000 times, a bac- 

 terium appears as a homogeneous particle, 

 with a sharp definite outline, though a mem- 

 branous envelope or wall, distinct from the 

 body of the bacterium, cannot at first be 

 recognized ; but when treated with reagents 

 a membranous envelope appears, the pres- 

 ence of which, without doubt, gives pre- 

 cision of form to the bacterium. The sub- 

 stance within the membrane contains gran- 

 ules which can be dyed with coloring agents. 

 Owing to their extreme minuteness it is 

 difficult to pronounce an opinion on the 

 nature of the chromatine granules and 

 the substance in which they lie. Some 

 observers regard them as nuclear material, 

 invested by only a thin layer of protoplasm, 

 on which view a bacterium would be a 

 nucleated cell. Others consider the bac- 



