INVOLUTION FORMS 



29 



branches are formed in a chain of bacilli when one near the centre 

 multiplies, and in doing so pushes the new bacillus formed out 

 of the line, so that it projects to either side, but still retains its 

 connection with the bacillus which produced it. 



Involution Forms. Bacteria often show very abnormal forms under 

 unfavorable conditions of growth, but these must simply be looked 

 upon as degenerates, or cripples. They are known as involution 

 forms. For example, the coccus of pneumonia on artificial culture 

 media shows long, irregular, bacilli-like forms; the anthrax bacillus, 

 which is a stiff, straight, cylindrical rod, becomes curved; the plague 

 bacillus in old cultures forms spermatozoa-like bodies, and the same 

 bacillus on an artificial culture medium (agar), containing 3 to 

 4 per cent, of common salt, forms large, round, yeast, cell-like 

 balls. In very old cultures bacteria undergo splitting up or frag- 



FIG. 12 



a b c d e f g h i 



Bacillus Biitschli: a to c, incomplete division of the cell; d to /, gradual collection of chro- 

 matin granules at ends of cells; g to i, formation of end spores from these chromatin end-masses. 

 (After Schaudinn.) 



mentation, and may finally break up into irregular granules. How- 

 ever, as soon as such involution forms are placed in fresh, good 

 culture media, under favorable conditions, they assume again their 

 normal shape, with all of their normal average properties. It is 

 only when unfavorable conditions are present, such as exhaustion of 

 the soils, accumulation of metabolic products, etc., that the foregoing 

 changes take place, otherwise bacteria always reproduce their own 

 type and are not polymorphous. Involution forms are, as a rule, 

 live bacteria, and if they are pathogenic they can produce their 

 specific disease. If inoculated into a fresh culture soil they will 

 reproduce the normal type of the species. 



Bacteria can be killed with chloroform or formalin vapors in such 

 a manner that they retain their shape perfectly. This should be done 

 when cultures of dangerous bacteria are placed in the hands of begin- 

 ners in the laboratory study of pathogenic microorganisms. 



