esterly: eucalanus. 5 



cutting paraffine sections. The treatment ordinarily given material 

 intended for microscopic investigation is sufficiently satisfactory in 

 this case, but to prevent shrinkage and distortion, care is necessary 

 in the use of the higher grades of alcohol, in clearing and in transferring 

 to paraffine. 



In dehydrating, I have made it a practice to transfer the material 

 from 90% alcohol to 95% alcohol and then after 5 or 10 minutes to 

 replace this by absolute alcohol. Xylol has proved to be the best 

 clearing agent. If this is added drop by drop to the absolute alcohol 

 until the mixture has reached the proportions of J alcohol and § xylol, 

 and then pure xylol is used, the animals will clear quickly and without 

 the least shrinkage. Before transferring to the paraffine used for 

 imbedding it is well to allow the object to remain for a time in a 

 saturated solution of paraffine in xylol. I have always used for 

 imbedding purposes a paraffine which melted at 60" C. and sections 

 were generally cut 10 /< in thickness, though sections 6 /i in thickness 

 are readily obtained. It is not necessary to employ a reagent for 

 softening or destroying the chitinous covering of the animal, for, after 

 any fixation employed, perfect sections and ribbons can be obtained. 

 The chief trouble has been to preserve the animal in its normal form, 

 so that it might be oriented for cutting sections in particular planes. 

 Dehydration and clearing take place very rapidly, but infiltration 

 with paraffine is slower. It is well to leave the animals in melted 

 paraffine for an hour or a little longer. 



I have relied chiefly upon a modification of one of vom Rath's 

 mixtures and upon Zenker's fluid for killing and fixing reagents. 

 Saturated aqueous corrosive sublimate and a corrosive-acetic mixture 

 have likewise been employed, as has also 10% formalin; but Zenker's 

 fluid is by far the most satisfactory of all these reagents. The osmic 

 acid mixture of vom Rath was modified slightly in the amount of 

 platinic chloride. To a mixture containing 12 c. c. of 2 % osmic acid, 

 100 c. c. saturated aqueous solution of picric acid, and 1 c. c. of acetic 

 acid, I added 25 c. c. of a 0.2% solution of platinic chloride. This 

 has given satisfactory results. It has been allowed to act for varying 

 lengths of time upon animals put into it from sea-Avater, and has in 

 some cases been followed by pyroligneous acid, as recommended by 

 vom Rath ('95). I believe it is better to allow the fixative to act alone 

 and for not more than 36 hours, otherwise the blackening is so great 

 as to detract from the value of the preparation. \'\^ien the fluid is 

 used for that time without further treatment the medullated nerve 

 fibres are blackened intensely, while the rest of the nervous system 



