588 Journal of Applied Microscopy. 



The Paraffin Method in Hot Weather. 



It is frequently desirable, or even necessary, to prepare sections for examina- 

 tion during the heat of the summer months. Those who have tried to handle 

 thin paraffin ribbons under such conditions of weather will appreciate the diffi- 

 culties of the process. During such heated periods, I have been obliged at times 

 to prepare slides, and driven to desperation by the unmanageableness of the 

 thin paraffin ribbons, I have tried various plans to obviate the difficulties 

 seemingly inherent in the methods. I was finally successful enough to obtain 

 good results, and, in the hope of helping some one else, I will here give the 

 simple means by which I operated. Most probably what I have to say will be 

 anything but new to many, but possibly the methods may come as suggestions 

 of value to some, and with that hope I will record them. 



The great difficulty, of course, arises from the approach of the room temper- 

 ature to that of the melting point of the paraffin, whereby the imbedding medium 

 is rendered so soft as to be unable to withstand the impact against the knife, or 

 to permit the handling of the ribbons without adhering to the instruments. Ob- 

 viously, the only way to succeed in the treatment of such a substance is to 

 render it cooler than the room ; for it is not ordinarily convenient to lower the 

 temperature of a room sufficiently, although this would be the more effective 

 escape from the difficulties. 



The means that render it possible to obtain good sections, even in the torrid 

 heat of summer, are haste and ice judiciously administered. First I place the 

 trimmed blocks of paraffin and their holders in a vessel containing cracked ice, 

 and the knife upon a cake of ice, until all become thoroughly cooled. I then 

 take a good sized crystallizing dish and fill it with small pieces of ice and place 

 over it a pane of glass. With everything thus in readiness, I place the holders 

 in the microtome, adjust the knife, and, as quickly as possible, cut the ribbons. 

 These, as they come from the block, are laid along the knife until of sufficient 

 length, when they are removed and spread upon the pane of glass over the ice. 



No difficulty will be found in keeping the block and the knife cool in the more 

 recent form of the Minot microtome, made in this country, where the knife rests 

 in a horizontal position, for it is easy to run the block up to the knife and to lay 

 a piece of ice upon the two. But in the older Minot with the knife set vertically, 

 it is more difficult to keep the cutting instrument and the object to be cut in the 

 proper condition of temperature. This, because the preliminary cooling will not 

 be found sufficient in cases where the block is of some size, and several 

 subsequent applications of the refrigerating agent therefore become necessary. 

 However, by exercising a little patience, I have succeeded with both machines, 

 and I am sure any one else can. 



With the ribbons cut and spread on the cool glass, it will not be found diffi- 

 cult to divide them into appropriate lengths for mounting, whereas, if they were 

 lying upon some substance at the temperature of the room, they would be found 

 to stick in a most uncomfortable manner, not only to the support but to the 

 cutting instruments. I found it most convenient to have the knife with which 



