232 STATE BOARD OF AGRICULTURE 



ment, thus making chemical agents impracticable. They, nevertheless, 

 have their use as sterilizers. It is possible to practically sterilize a sur- 

 face of wood, as the floor, the table, etc., and they are fitted for cleansing 

 walls and ceilings. Metallic surfaces maybe purified, and surgical instru- 

 ments rendered aseptic — free from bacteria producing diseased conditions. 

 These chemicals may not kill the bacteria, but they do prevent their 

 growth, which is a form of practical sterilization. A vessel may be steri- 

 lized with chemicals and the chemicals then washed out with sterilized 

 water. Chemical sterilizers fit in where other means cannot be employed. 

 The substances used for this purpose will be considered in another bulle- 

 tin, which will follow later, taking up germicidal agents and disinfectants 

 for farm use with practical application. Chemicals as absolute sterilizers 



are of very limited application. 

 FUtration. gy ^]^ig jg ^q^ meant filtration by the ordinary filters of char- 



coal or sand, nor any improvised filter for temporary use. Such 

 filters may be able to remove suspended particles of matter and assist in the 

 oxidation of organic matter, but they will not remove bacteria. 

 Porcelain There is only one filter that will strain out the bacteria; this is 

 moulded from a fine plastic substance, and is baked at a very 

 high temperature. There is produced an unglazed porcelain. 

 If perfect, the finest particles, not even bacteria, will pass through this 

 filter, but the liquid will, when under pressure; without pressure it would 

 pass through impracticably slowly. To apply pressure the porcelain is 

 made in the forms of long tubes, which are placed in cylinders containing 

 the material for filtration. The top is fitted closely to allow pressure upon 

 the liquid in the cylinder; this pressure forces the liquid through the 

 porcelain into the inner side of the tube, where it is perfectly free from 

 organic particles or bacteria, as the case may be. All the suspended mat- 

 ter adheres to the outer surface, from which it is easily removed. 



Filtration of this kind is resorted to in the study of products, formed by 

 the action of bacteria. This filter is also used largely in the filtration of 

 drinking water. For this purpose it is strongly recommended, provided 

 the filters are without flaws. It has been highly praised where it has been 

 used on a large scale in furnishing water to the inhabitants of villages. If 

 India, where this work is in operation, were to make universal use of them, 

 the mortality from Asiatic cholera would doubtless be reduced to a frac- 

 tion of one per cent. 

 Cottonwool. Yov filtration of air in cultural work, ordinary cotton-wool is 

 utilized. This will not free the air of bacteria if a very strong 

 current is forced through. The bacteria apparently lodge in its meshes 

 before reaching the media within. To illustrate what cotton-wool will do 

 in arresting minute organisms, an early experiment with fermentation may 

 be cited. In order to demonstrate the action of yeast plants upon sugar 

 solutions, a tube was filled with a very weak solution of sugar, containing 

 some nitrogenous matter. It was rendered free from bacteria and yeast 

 plants and a sterilized piece of cotton-wool was inserted half way down 

 the tube. The yeast plant was added to the upper half but the lower half 

 was left uninoculated. The upper half fermented and the lower half 

 remained unchanged, showing that the cotton-wool formed a perfect bar- 

 rier to the yeast plant. It was in about 1854 that it was first used and 

 now it is almost exclusively employed to close culture tubes against infec- 

 tion from the outside. 



