4 TEXT-BOOK OF BACTERIOLOGY. 



If we examine the same variety of bacilli which have been de- 

 veloped a.t a low temperature on the surface of a slice of boiled 

 potato, they can scarcely be recognized. It is, therefore, evident 

 that this kind of nourishment is unsuitable for their development, 

 as we find all sorts of irregularly-developed cells and amorphous 

 bodies massed together, with here and there a long cylinder, which 

 reminds one of what the anthrax cell should be. We also see numer- 

 ous distinctly rounded forms of bacteria, which might be mistaken 

 for cocci. 



Do such cells, therefore, belong in the circle of development of 

 the anthrax bacilli? Certainly not. For if we bring them into 

 favorable conditions of nourishment, it will be seen either that they 

 are no more capable of propagation — that we, therefore, have to do 

 with dead substances — or, on the other hand, that they immedi- 

 ately give birth to the described typical forms of growth, the long 

 rods of regular shape. These forms were, indeed, nothing but the 

 expression of degeneration in the bacteria in question. They are 

 degenerative forms, or, as Nageli has called them, "involution 

 forms," malformations which are not to be mistaken for the healthy 

 bacilli. 



While the species of bacteria which we have just considered 

 adhere, with a most remarkable tenacity, to that peculiar form 

 (which they keep under all circumstances), there are others which 

 seem to take a peculiar delight in developing strange forms, which 

 degenerate more frequently than others, quitting their normal ex- 

 ternal forms, and in preparations exhibiting features calculated to 

 puzzle for the moment even the most practised observer. Now, 

 these changes are not a necessary, inevitable step in the changes 

 which the individual must assume during its growth, but simply a 

 sign that under the influence of unfavorable circumstances a degen- 

 eration of the bacterial protoplasm has taken place. 



This is just what is meant by the expression "constancy of 

 form ; " that a species of bacteria, under varied conditions of life, 

 may change its external appearance, its form, more or less; but 

 under all circumstances a clearly describable form exists, in which 

 this species finds the expression for the maximum of its development, 

 the climax of its well-being. It is of course possible that future 

 researches may point out an exception or exceptions to the above 

 rule. Among the lowest vegetable organisms which stand nearest 

 bacteria, some have been known to botanists which certainly pos- 

 sess the capability of going through a tolerably wide metamor- 

 phosis. These are chiefly water-pieces — the crenothrix, cladothrix, 

 and beggiatoa, which, under some circumstances, appear as long 



