42 MORPHOLOGICAL CHANGES DURING GROWTH 



During the early latent period, when growth is slow or completely lacking, no apparent 

 morphological change is seen. Following this, during the logarithmic period when 

 maximum reproduction occurs, the cells from the young cultures of many genera of 

 bacteria attain their maximum size, two to six times larger than the cells from the 

 twenty-four-hour parent-cultures. After four to eight hours the cultures pass gradu- 

 ally into the stationary period, in which the number of organisms remains relatively 

 constant. During this progression to the stationary period, the bacteria become 

 gradually smaller in size until, by the time the cultures are eighteen to twenty-four- 

 hours old, the classical textbook picture is presented. Cultures older than twenty- 

 four and forty-eight hours present more and more of the so-called "involution forms," 

 irregular staining, in many instances bizarre forms, and organisms averaging smaller 

 than those found in the twenty-four-hour cultures predominate. 



Clark and RuehP studied by this method seventy strains in all, including cultures 

 of the following species: 



COCCACEAE Strains 



Staphylococcus aureus 5 



Staphylococcus albus 2 



Streptococcus hemolyticus 6 



Diplococcus pneumoniae 5 (including types I, II, and III) 



Neisseria gonorrheae 



Neisseria catarrhalis 2 



Neisseria intracellularis 



Neisseria mucosis 

 Spirillaceae 



Vibrio comma 



Vibrio metchnikovi 



Vibrio schuylkilliensis 

 Bacteriaceae 



Proteus vulgaris 



Escherichia coli 



Escherichia communior 



Eberthella typhi 5 



Eberthella dysenteriae 



Eberthella paradysenteriae 



Salmonella paratyphi 



Salmonella schottmiilleri 



Salmonella suipestifer 



Encapsulatus pneumoniae 2 



Pseudomonas pyocyaneus 



Serratia marcescens 



Pasteurella avicida 



Hemophilus influenzae 



Hemophilus pertussis 



Bacillus anthracis 



Bacillus subtilis 



Bacillus megatherium 



' Clark, P. F., and Ruehl, W. H.: loc. cit. 



