324 Journal of Applied Microscopy. 



the chloroform. Not infrequently the chloroform itself is at fault, as it may also 

 contain a slight amount of water. This difficulty is obviated or lessened by 

 using pure acetone and pure chloroform. Those using the oil method of cutting 

 collodion sections may abridge the process still further by omitting the use of 

 the chloroform and immersing directly in the clarifying agent. 



Incompatibility. — The question of incompatibility with the fixing agents 

 ordinarily used is of considerable importance, but the fact must be kept well in 

 mind that an incompatibility with a solution of the fixing agent when acetone is 

 mixed with it, may be of quite a different character than when the tissue, 

 hardened in the fixing agent, is brought in contact with acetone. 



There is always some reaction between the protoplasm of the tissue and the 

 fixer ; the formation of various albuminates, etc. ; as for example, when an equal 

 amount, or excess, of acetone be added to a solution of potassium dichromate, 

 a slight precipitate is formed, but not nearly equal, in amount, to the precipitate 

 thrown down when alcohol is added to a solution of dichromate. If, on the 

 other hand, a piece of tissue hardened in the dichromate be immersed in acetone, 

 there is no perceptible precipitate for a long time, although the acetone takes on 

 a yellowish tinge from the salt. The range of incompatibility, so far as deter- 

 mined, is decidedly less than that of alcohol. 



Cost. — The cost of the chemically pure acetone averages from eighty to 

 ninety cents per pound. Many specimens of the commercial acetone, however, 

 seem to be quite free from water and to answer the purpose just as well as the 

 chemically pure for histological uses, with the further advantage that its cost is 

 only thirty or thirty-five cents per pound ; and still lower rates may be obtained 

 if bought in larger quantities. 



To private workers, especially, who are not able to avail themselves of the 

 facilities of college laboratories, the use of acetone would seem to be of consider- 

 able benefit. It is easy to procure ; it is much cheaper than the usual ether- 

 alcohol mixture, and shortens the process. 



Acetone should not be confounded with aceton, — the latter being a proprie- 

 tary grip and headache remedy. 



Pierre A. Fish, D. Sc, D. V. S. 

 New York State Veterinary College, Ithaca, N. Y. 



Demonstration of Karyokinesis. 



In dealing with large classes, the satisfactory illustration of the process of 

 karj-okinesis is not easy owing to the difficulty in obtaining material which has 

 the elements of the mitotic figure large enough to be made out with the ordinary 

 student microscope, and which is undergoing division rapidly enough to show 

 many different phases of the process within a single section or a limited number 

 of sections. In animal tissues these conditions are best met perhaps by the 

 testis of the cray-fish or lobster taken at the breeding season. By reason of the 

 large size of the chromosomes, certain plant tissues also, such as the growing 

 tip of the onion, have become favorite demonstration objects with biologists. 

 Excellent for the purpose as these objects are, they are nevertheless much 



