58 



Messrs. Barnard and Hewlett. Method of [Mar. 28, 



cell with the sand particle ruptured the cell wall and caused the contents of 

 the cell to be expelled. 



The objection to this method is that a great rise of temperature rapidly 

 takes place unless very efficient means are adopted for cooling ; in fact, the 

 whole mass may quickly reach boiling point unless this is efficiently per- 

 formed. The cooling method they employed was to surround the containing 

 vessel with brine at a temperature of about —5° C, which sufficed to keep 

 the yeast mass at a temperature of about 15° C. Macfadyen and Eowland 

 later discarded this method, and adopted one in which micro-organisms were 

 disintegrated at the temperature of liquid air, and described their method in 

 a paper on " The Intracellular Constituents of the Typhoid Bacillus."* In 

 this apparatus the organisms in mass are placed in a cylindrical metal 

 vessel, which is itself immersed in a vessel of liquid air. The inner 

 container has a conical-shaped bottom, and in this another cone fits which 

 is caused to rotate and is also free to move vertically. On placing the 

 mass of bacterial or other cells in -the container, the cells are rendered 

 extremely brittle by the low temperature of the surrounding liquid air. The 

 cone is caused to rotate inside the container and at the same time to move 

 up and down, engaging at each rise and fall a number of the cells between 

 the bottom of the containing pot and itself. The result is that each time 

 a proportion of them is fractured. The sequence of operations is continued 

 until the micro-organisms are found on microscopical examination to be 

 disintegrated. On the completion of the process the temperature of the mass 

 is allowed to rise, salt solution is added if necessary, and the suspension is 

 then centrifugalised so that the cell bodies and any metallic contamination 

 are removed. The amount that may be dealt with by this method is not 

 large, varying usually from 05 to 1 grm., and the time required for the 

 complete disintegration of such a quantity varies from one and a half to 

 two hours. 



Subsequent experiments have shown that while it is necessary to maintain 

 the material at a low temperature to ensure the brittleness of the cell and to 

 prevent chemical change during the process, such a low temperature as that 

 of liquid air is not essential. 



It appears to the writers that the conditions to be fulfilled in designing an 

 efficient machine for the disintegration of micro-organisms are as follows : — 



1. The grinding should be effected in a manner which is, as far as possible, 

 frictionless, so that the risk of rise of temperature and consequent chemical 

 change is avoided so far as possible, even apart from any extraneous cooling 

 arrangement. 



* ' Centralblatt fiir Bakteriologie,' 1903, No. 8. 



