102 ALEXANDER L. BOUNCE 



A second drawback of the Hagan-Potter-Elvehjem instrument is that 

 an unknown degree of local heating by friction may occur at the grinding 

 surfaces when homogenization is protracted, and this friction also may 

 cause a small amount of ground glass to be introduced into the homog- 

 enate. In the experience of the writer, the Hagan-Potter-Elvehjem homog- 

 enizer, which by universal agreement is excellent for work in isolating mito- 

 chondria and microsomes, is not a good homogenizer for work in isolating 

 cell nuclei. 



A small-scale homogenizer has recently been devised in the writer's lab- 

 oratory which can be used for preparing cell nuclei or mitochondria and 

 which, for soft tissues, is superior to any homogenizer described in the litera- 

 ture in sufficient detail to be easily constructed. This homogenizer functions 

 best with relatively soft tissue such as liver or pancreas, but it could pos- 

 sibly be used on tougher tissue if the latter were first squeezed through 

 small openings, as in the apparatus shown in Fig. 1. 



The homogenizer is constructed of heavy -walled glass tubing and glass 

 rod. The tubing is ground cylindrical on the inside. Precision-bore glass 

 tubing would presumably be an excellent substitute for the ground tubing 

 if it could be obtained with sufficiently thick walls. A bulb blown near 

 the top of the tube acts as a reservoir. The pestle is constructed of heavy 

 glass rod with a round ball on the bottom end and a short thick crosspiece 

 at the top for grasping with the hand. The ball is made very slightly over- 

 size and is fitted to the cylinder by grinding with fine carborundum (number 

 400 or number 600) . After grinding, the ball is cautiously fire-polished to aid 

 in avoiding excessive wear. The homogenizer is inserted in a hole in a large 

 rubber stopper which serves as a base, and is immersed in a bath of ice and 

 water before use. The operation is manual, the pestle being simply pushed 

 down and pulled up without rotation. It is a good plan to start the homog- 

 enization with a rather loosely fitting pestle, using about half a dozen 

 strokes, and then, after filtering to remove fiber, to change to the more ex- 

 actly fitting pestle which should operate Avith a clearance in the neighbor- 

 hood of 0.5-thousandths of an inch or slightly less. From six to thirty-six 

 strokes of the well-fitting pestle may be required for complete homogeniza- 

 tion, depending upon the tissue and the medium used. Since this requires 

 considerable effort, it might be desirable to fit the plunger with a lever, but 

 we have not found it necessary to do so. The barrel of the homogenizer should 

 be filled not quite to the bottom of the bulb for best results. A diagram of 

 this homogenizer is shown in Fig. 2. A similar homogenizer no doubt could 

 be built on a considerably larger scale from stainless steel. 



The principal advantage of the homogenizer just described is that a tight 

 fit may be obtained between the ball and cylinder wall without rendering 

 the plunger immovable. This is because the space between the ball and cyl- 



