HERBERT C. WARD 3 



these organisms. Reed and Orr' attribute such morphological changes to the influence 

 of the hydrogen-ion concentration in the media. Any acidity or alkalinity close to the 

 limiting reaction for successful cultivation leads to the appearance of these aberrant 

 forms. Changes in morphology cannot be attributed solely to the influence of the hy- 

 drogen-ion concentration since Vay' had previously found that the addition of dyes 

 like dahlia to the media leads to the production of long dye-stained threads by Bacillus 

 typhosus and Bacillus paratyphosus. According to Henrici,^ who has studied the in- 

 volution forms in Bacillus coli especially, variation in morphology seems to correlate 

 with autolysis of dead cells. The rate of autolysis depends upon the degree of acidity 

 or alkalinity of the medium. 



That bacteria may have different sizes at different stages has long been suspected. 

 Evidence substantiating this view has been presented by Clark and Ruehl, and by 

 Henrici. Clark and RuehP have noted that in general very young bacteria, in the 

 first few hours of growth, are much larger than older organisms. This does not hold 

 for all species, however, since these authors found that this enlargement does not occur 

 with diphtheria and glanders bacilli. Henrici^ has found that morphological variations 

 occur in the lag period of bacterial growth. The initiation of growth is marked by a 

 transformation to embryonic or growing cells which are considerably larger than the 

 cells produced during the phase of maximum development. 



The production of large, irregular involution forms regarded as characteristic of 

 the plague bacillus has been found by Smillie^ in other representatives of the hemor- 

 rhagic septicemia group. This work has not thus far been definitely confirmed. In- 

 volution forms occur with such species as Bacillus suisepticus, but they are not as 

 marked as are those in Bacillus pestis. 



Finally, a new point of view in regard to the branching of bacteria has been 

 brought out by Gardner^ who believes that probably many pathogenic bacilli grow by 

 three-point branching from Y-shaped forms. If Gardner's observations can be con- 

 firmed they will give us a different conception of bacterial multiplication and may ex- 

 plain many obscure points in morphology and physiology. 



FILTERABLE FORMS OF BACTERIA 



Under ordinary circumstances the passage of bacteria through the pores of filter 

 material like the siliceous earth in Berkefeld candles and the unglazed porcelain in 

 Chamberland bougies depends on the size of the pores and the size of the bacteria, al- 

 though other factors of great importance may modify the results. The most important 

 of these are the amount of pressure or suction applied to force the fluid through the 

 filter mass, the composition of the fluid in which the bacteria are suspended, and its 

 reaction. At the same time the type of the micro-organisms has an important influ- 

 ence on their ability to pass through filter material, and it has long been recognized 



' Reed, G., and Orr, J. H.: J. Bad., 8, 103. 1923. 



*Vay, F. : Cenlralbl.f. Bakteriol., 55, 193. 1910. 



3 Henrici, A. T.: /. Infect. Dis., 39, 429. 1926. 



" Clark, P. F., and Ruehl, W. H.: /. BacL, 4, 615. 1919, 



s Henrici, A. T.: /. Infect. Dis., 38, 54. 1926. 



* Smillie, W. G.: ibid., 27, 378. 1920. ^ Gardner, A. D.: /. Path. 6* Bad., 28, 189. 1925. 



