lOO MOEPHOLOGY AND CULTURE OP MICROORGANISMS 



small grains, which generally increase gradually in size during de- 

 velopment, and finally are absorbed in the very old cells. They are 

 sometimes distributed through the whole cell {Spirillum volutans) as 

 grains of chromatin (Fig. 76, 8 and 9), but most often they tend to 

 gather at the two poles of the cell, or line up aU along the bacillus 

 (Fig. 76, I to 4, 6, 10, 11). In some species {B. alvei, aster osforus, 

 Bad. tuberculosis and diphtherice) , these corpuscles grow bigger until 

 they attain relatively large dimensions, surpassing the baciUus in size. 

 Thus they cause a series of swellings all along the bacillus, which in 

 consequence appears somewhat like a necklace (Fig. 76, 11). They 

 then give the illusion of spores; one can easily understand the error 

 of some authors who have confused them with spores, notably in the 

 case of the Bad. tuberculosis. 



In B. asterosporus, the metachromatic corpuscles usually appear in 

 the youngest cells, singly and in the shape of a small central granule 

 closely resembling a nucleus and which A. Meyer seems to have taken 

 for such (Fig. 76, 5). 



During sporulation, the metachromatic corpuscles exist just out- 

 side of the spore (Fig. 76, 7), then are finally absorbed by it. They 

 therefore act like reserve products. 



Moreover, in the cells of bacteria other reserve products, notably 

 globules of fat and of glycogen, have been found. 



Bacterial Cell Wall. — General Structure.* — AU the bacteria have 

 cell walls and it is these that give definite form to the cell. These walls 

 are rigid and elastic and are probably made up of two layers, the outer one 

 of which is able to deliquesce and form capsules, or perhaps zooglcea. 

 The inner part retains the elasticity and gives the form to the bacteria. 

 These cell walls are readily permeable to water and it is through 

 them that all of the nourishment of the cell is obtained; that is, 

 there are no openings for the entrance of food or the discharge of 

 by-products, but the intake and output goes on through the cell wall 

 which is entire. 



Minute Structure of Cell Wall.'f — In some species of large sizej 

 the membrane can be distinguished when strongly magnified, and 

 appears with a double contour. Usually it is scarcely visible, and can 

 be observed only when the contents of the cell has been contracted by 



• Prepared by W. D. Frost. 



t Prepared by A. Guilliermond. 



