BLACKMAN : THE SPERMATOGENESIS OF SCOLOPENDRA. 5 



the fixation in favorable material is apparently perfect. There is no 

 perceptible shrinkage, and at least the grosser structure of the cells is 

 identical with that observed in living cells derived from the same 

 source. 



The material was left in this killing fluid for lengths of time varying 

 from twenty-four to sixty hours. Probably the best results were ob- 

 tained with material fixed forty-eight hours, although there is little 

 apparent difference due to variations in the length of exposure. It is 

 always well to use a large amount of fluid, thirty to fifty times the vol- 

 ume of the object, and if left for more than twenty-four hours in the 

 fixing reagent, this should be renewed. After fixation the objects were 

 washed for several hours in running water and then gradually dehy- 

 drated in alcohol of the grades of thirty per cent, fifty per cent, and 

 seventy per cent. To remove the sublimate and prevent the formation of 

 crystals, a few drops of an alcoholic solution of iodine were added to the 

 seventy per cent alcohol. 



In order to obtain the best results with material fixed in Gilson's mix- 

 ture, I have found that it is necessary to employ for infiltrating and 

 embedding, the combined celloidin and paraffin method described in a 

 former paper (Blackman, :01, p. 62). While this fixation if properly 

 carried out is nearly perfect, it leaves the tissues very soft, so that, if 

 the ordinary paraffin method is employed, some shrinkage must inevi- 

 tably occur. With the celloidin-paraffin method this disadvantage is 

 obviated. 



The sections were cut with the Minot precision microtome, the thick- 

 ness varying from 2 to 6 ruicra, and were affixed to the slide in the or- 

 dinary manner by using very dilute albumen water (two drops of 

 Mayer's albumen to one ounce of distilled water). Then the paraffin 

 was removed by means of xylol and the sections stained as noted later. 

 In the finer work it was found desirable to remove the celloidin also. 

 This may be done, either before or after staining, by placing the slide 

 for a few minutes in a mixture of absolute alcohol and ether. 



In staining the sections a number of methods were used. The draw- 

 ings and photomicrographs accompanying this paper were made exclu- 

 sively from sections stained in Heidenhaiu's haematoxylin, either used 

 alone or in conjunction with Congo red. For microchemical tests, Bis- 

 mark brown, cyanin, methyl green, Auerbach's raethyl-green-acid-fuchsin, 

 Flemming's three-color stain, and numerous other dyes were used. For 

 the study of the chromatin structures the preparations stained with 

 Heidenhain's haematoxylin were the most favorable, although in some 



