TWENTIETH ANNUAL MEETING. 



85 



They consist of single elon- 

 gated or spherical cells, and 

 increase in number by a process 

 of transverse fission. The cells 

 increase to about double their 

 original size, the middle portion 

 becomes constricted, and two 

 cells are thus formed from one. 

 In some instances they remain 

 attached for periods of more or 

 less extent, forming long slender 

 threads. They can move about 

 by means of slender filaments at 

 each end of the body. 



The bacteria are found in all 

 decaying and fermenting sub- 

 stances. They are divided into 

 four groups, according to their 

 form. In the first we have those 

 consisting of spherical cells. 

 They are very minute and 

 belong to the genus micrococcus. 

 This organism in its various 

 forms gives rise to many dis- 

 eases to which mankind is 

 subject, among them being diph- 

 theria. Another form causes 

 what is known as fireblight in 

 our pears, and twig blight in 

 apples, pears, and quinces. 



So far as is now known, the only 

 remedy is to remove and burn 

 the affected portions, cutting at 

 least a foot below where any 

 sign of the disease can be 

 seen. 



The microbes gain entrance to the tree through wounds in the bark, 

 through the watery, unripened. growth at the ends of the new shoots, and 

 through the unprotected stigmas of the flowers. As preventives, avoid 

 the use, for pears, of nitrogenous manures, or soils containing an excessive 

 amount of organic matter; plant varieties that naturally grow slowly and 

 whose wood is firm ; train with low heads, and, so far as is possible, protect 

 the trunk and branches from the burning rays of the sun. In dry seasons, 

 especially if the trees are bearing full crops of fruit, secure for them by 

 frequent shallow cultivation, or by mulching, an abundance of moisture, 

 that the branches may not become dry and crack, thus affording access to 

 the germs. 



Of the other genera we have the bacterium (Fig. 2, ^-), with its 

 straight, rod-like body, found in all putrefying bodies; the bacillus (Fig. 

 2, *), the active agent in consumption, anthrax, cholera, and other diseases; 

 the vibrio (Fig. 2, ^), differing from bacillus in having curved filaments; 

 the comparatively large, coiled, and twisted Spirillum (Fig, 2, ^); and the 

 finely-coiled Spirochsete (Fig. 2, '). 



Fig. 2.— Schizomycetes oh Bacteria. 



1. Micrococcas. 



2. Bacterium. 



3. Bacterium, zoOgloea stage. 



4. Bacillus. 



5. Vibrio. 



6. Spirillum. 



7. Spirocheete — After Colin. 



