BROWNIAN MOVEMENT 11 



only in different species, but even in the same species 

 when grown on different nutrient media. All bacteria 

 contain proteins, lipoid substances, and salts. Bacterial 

 protein, according to Nencki, differs from ordinary protein 

 matter in not being precipitated by alcohol and in not 

 containing sulphur ; it was termed by him " myko- 

 protein." This does not appear to be the case with the 

 proteins obtained by grinding bacterial cells, which seem 

 to agree with other proteins in heat-coagulation, etc. 



The proteins are mainly globulins and nucleo-proteins. 

 The cell wall is relatively insoluble, and generally consists 

 chiefly of a material like ckitin, and not of cellulose ; in 

 this respect bacteria resemble animal rather than vegetable 

 cells. Carbohydrates are generally scanty. Spores differ 

 from the parent cells in containing a larger proportion of 

 solids and less water. 



All species of bacteria, but especially the smaller ones, 

 when suspended in a fluid exhibit what is known as. 

 Brownian movement, consisting of an oscillation with 

 some amount of rotation about a fixed point, but there 

 is little actual movement of translation, unless due to 

 flotation. This Brownian movement is physical and not 

 vital in origin, and occurs with all fine particles suspended 

 in a fluid, and must be clearly distinguished from a true 

 vital motility. 1 Some bacteria are always motionless, 

 others are more or less motile, but these, too, have a 

 resting stage. For motility to occur the cells must be 

 young, and the conditions favourable to growth and 

 development. Motility is due to delicate protoplasmic 

 threads termed " flagella " connected with the outer layer 

 of the cell protoplasm ; these vibrate to and fro and 

 propel the organism through the medium. A cell will, 



1 Brownian movement is due to " the incessant movements of the 

 molecules of the -liquid which, striking incessantly the observed par- 

 ticles, drive them about irregularly through the fluid " (Perrin). 



