MOTILITY. 9 



all motile forms. There is little doubt, however, that all cases 

 of motility among the bacteria are not dependent on the posses- 

 sion of fiagella, for in some of the special spiral forms, and in 

 most of the higher bacteria, motility is probably due to contrac- 

 tility of the protoplasm itself. 



The Minuter Structure of the Bacterial Protoplasm. — Many attempts have 

 been made to obtain deeper information as to the structure of the bacterial 

 cell, and especially as to its behaviour in division. These have largely turned 

 on the interpretation to be put on certain appearances which have been ob- 

 served. These appearances are of two kinds. First, under certain circum- 

 stances irregular, deeply stained granules are observed in the protoplasm, 

 often, when they occur in a bacillus, giving the latter the appearance of a 

 short chain of cocci. They are often called metachromatic granules ivide 

 Fig. I, No. i6) from the fact that by appropriate procedure they can be 

 stained with one dye, and the protoplasm in which they lie with another ; 

 sometimes, when a single stain is used, such as methylene-blue, they assume 

 a slightly different tint from the protoplasm. 



For the demonstration of the metachromatic granules two methods have 

 been advanced. Ernst recommends that a few drops of Loffler's methylene- 

 blue {vide p. I go) be placed on a cover-glass preparation and the latter passed 

 backwards and forwards over a Bunsen flame for half a minute after steam 

 begins to rise. The preparation is then washed in water and counter-stained 

 for one or two minutes in watery Bismarck-brown. The granules are here 

 stained blue, the protoplasm brown. Neisser stains a similar preparation in 

 warm carbol-fuchsin, washes with i per cent sulphuric acid and counter-stains 

 with Loffler's blue. Here the granules are magenta, the protoplasm blue. 

 The general character of the granules thus is that they retain the first stain 

 more intensely than the rest of the protoplasm does. 



A second appearance which can sometimes be seen in specimens stained 

 in ordinary ways is the occurrence of a concentration of the protoplasm at each 

 end of a bacterium, indicated by these parts being deeply stained. These 

 deeply stained parts are sometimes called polar granules (vide Fig. i. No. i6, 

 the bacillus most to the left), (German, Polkornchen or Polkbrner). 



With regard to the significance that is to be attached to such appearances, 

 much depends on whether they are constantly present under all circumstances, 

 or only occasionally, when the organism is grown in special media or under 

 special growth conditions. Some bacteria, however stained, show evidence 

 of having the protoplasm somewhat granular. In other cases this granular 

 condition is only seen when the organism has been grown under bad conditions, 

 or where the food supply is becoming exhausted. Some have thought that 

 the appearances might be due to a process allied to mitosis, and might signify 

 approaching division, but of this there is no evidence. 



In perfectly healthy and young bacteria, moreover, appearance of granule 

 formation and of vacuolation may be accidentally produced by physical means 

 in the occurrence of what is known as plasniolysis. To speak generally, when 

 a mass of protoplasm surrounded by a fairly firm envelope of a colloidal nature 



