i66 MICRO-ORGANISMS AND DISEASE [chap. 



rounded outline, spherical or oval in shape, and represents a 

 \acuole ; occasionally the stained protoplasm is central, 

 while the unstained parts, the vacuoles, are terminal. Such 

 vacuoles are very common in all species of bacilli ; they 

 (vacuoles) are, liowever, more frequently met with under 

 conditions which imply want of sufficient nutritive material, 

 as, for instance, when bacilli grow on solid media (gelatine, 

 Agar mixture, potato) and when, owing to the continued 

 growth into the depth of the medium, the first-formed or 

 superficial layer becomes gradually removed from the nutri- 

 tive material ; in this superficial layer the vacuoles in the 



Fig. 42. — The same Bacillus as !:•; treceding figure. 

 At I, spores ha\-e made their appearance. 



rods are very conspicuous ; in preparations made of thread- 

 forming bacilli under the above conditions of growth these 

 appearances, i.e. of the presence of vacuoles regularly 

 disposed in the individual rods, are very striking. 



But, as stated before, the presence of vacuoles in the rods 

 is also found under other than the above conditions, in 

 some species more numerously than in others, and more 

 often where rapid growth takes place than where this is not 

 the case. This vacuolation is not indicative of any degenera- 

 ti\'e change, any more than it is in the mycelial threads of 

 fungi where it is well known and typical, but seems, in 

 some cases at any rate, to be due to the medium in which 



