. , VETERINARY !> AT H( 1L( IGY. 



then they divide, i. e., a cell divides into two equal halves, each 

 half representing an individual bacterium which in turn (rows 

 and ultimatelv divides into two equal halves, etc., thus bacteria 

 grow and nuiltiplv. The rate of growth and division is com- 

 paratively rapid. The Bacillus subtilis, under favorable con- 

 ditions may pass through the life cycles incident to attaining 

 its growth and dividing, thus doubling in number, every :!i} min- 

 utes. Barber has found that Bacillus coli communis, under 

 optimmn conditions may divide by fission, in seventeen min- 

 utes. Beginning witli one bacterium, it has been estimated that 

 if division occurred once per hour and continued for three days, 

 the progeny would \\'eigh 7,-11^ tons. Some other cells, notably 

 the undifferentiated cell in the animal embryo, may divide as 

 rapidlv as bacteria, but tliev do not become developed, and so 

 far as known, there arc no other cells that complete the entire 

 cycle of growth and re])roduction in so sh(3rt a time. This 

 method <>f re])r(iducti(in is called fission. Fission occurs in the 

 three principal forms of bacteria. Among the Bacteriaceae and 

 Spirallaceae, the division takes place m the transverse diameter, 

 -v\-hile the Coccaceae mav divide in one, two or three planes. 



I'lJ — Bacteria, shuwins fission. 



Bacteria grow and divid.e bv fission as long as favorable 

 conditions are supplied. When the environments are unfavor- 

 able the organisms cease growing and do not increase in num- 

 ber. Sc)me species produce spores when conditions become 

 unfavfirable for further growth and fission. Bacterial spores. 

 generalK" characterized by being small, highly refractive oval 

 shaped bodies, are more condensed than the original cell body 

 protoplasm. Spore formation is first indicated by the appearance 



