SPORULATION OR SPORE FORMATION 35 



formly colored, others stain in such a manner that dyed portions 

 alternate with undyed sections of the entoplasm. Some bacilli take 

 the stains easy, others with difficulty. 



Size of Bacteria. Microscopic Measure. Bacteria are, as a rule, 

 exceedingly small in size, their longest diameter being only a fraction 

 of the diameter of a mammalian red blood corpuscle, and they can be 

 studied individually only by the aid of good compound microscopes. 



The size of bacteria is expressed by a microscopic measure based 

 upon the metric system: 



1 meter (about forty inches) = 100 centimeters = 1000 millimeters. 



1 millimeter = 1000 micromillimeters. 



1 micromillimeter or micron = about 2~5iroir i ncn - 



The term micromillimeter is indicated by the Greek letter p or 

 abbreviated micron (plural micra). 



Sporulation or Spore Formation. Under certain conditions, par- 

 ticularly when the soil in which bacteria have grown abundantly 

 becomes exhausted, and when the metabolic products have accumu- 

 lated, spore formation occurs. The spore of a bacterium may be 

 likened in a certain sense to the seed of a higher plant. Only a 

 limited number of the disease-producing bacteria form spores, and 

 these are nearly all bacilli, very rarely cocci and spirilla. Spore 

 formation is sometimes dependent upon very definite conditions, for 

 instance, the anthrax bacillus requires the presence of free oxygen. 

 Because these spores are formed in the interior of the bacterium 

 they are known as endospores. Bacteria do not multiply by sporu- 

 lation, since there is only one spore formed. However, this is not 

 an absolute rule; exceptionally two spores have been found in one 

 bacillus, but this occurrence is so very rare that it may be neglected 

 entirely for any practical consideration. Spore formation is very 

 important in the life history of bacteria, because the spores are very 

 resistant to external inimical influences, and can stand antiseptics 

 and heat very much better than the full-grown or vegetative form 

 of the bacterium. In fact, some spores, as, for instance, those of the 

 bacilli of tetanus, malignant edema, black-leg, and some soil bac- 

 teria, represent the most resistant organisms known. In order to 

 kill tetanus spores with certainty they must be exposed for over an 

 hour to the temperature of boiling water or steam at 100 C. This 

 great resistance enables spores to survive where the adult vegetative 

 form of the bacterium would perish. On account of their great 

 resistance, spores in German are known as Dauerformen, which 

 means durable forms of the bacterium. The great resistance of 

 spores is largely due to the fact that they possess a very firm, tough, 

 protecting membrane. In shape they are either round or oval, and 

 are situated at either the centre or at or near one of the ends of the 

 bacterium. Spores situated at one end of the bacterium, like that of 

 the tetanus bacillus, give to the small rod the appearance of a drum- 

 stick. Spores situated in the centre, and making this part bulge out, 



