METHODS OF INVESTIGATION. 35 



changiug tlic fluids care is necessary never to allow these to drain 

 off from the cavities of the object. The inclusion of air-bubbles 

 can be prevented by effecting the transference slowly until the 

 new fluid covers tlie object. 



Specimens fixed in the above way can be most readily 

 stained, for which purpose I have extensively used Gkenacuer's 

 borax-carraiue and Kleinenbekg's or Delafield's hsematox- 

 ylin in preference to either alum-carmine or picrocarmiue. 

 Beautiful as were the luematoxylin preparations, these seemed 

 to show no particular merit over the results attained by the 

 borax-carmine, and the latter has been more commonly em- 

 ployed for general purposes as giving more durable and more 

 uniformly successful results. As a weakness of all the staiuiug 

 fluids above referred to, it may be mentioned that they do not 

 always color the protoplasm of the tissues with desirable inten- 

 sity. I felt this shortcoming especially in clearly making out 

 the structure of the chamber-wall. In such cases, however, good 

 results were achieved by staining once again, after laying out 

 into sections, with a so-called plasma stain (f. i., acid-fuchsin). 

 Even in the case where staining after cutting is preferred, I 

 have often found it advisable to give a faint coloring to the 

 object before imbedding ; for, colorless pieces of the sponge be- 

 couie almost invisible in the paraffine, making the orientation of 

 parts difficult or impossible. 



For imbedding I have gone through the usual steps. Re- 

 moving the alcohol with lurpentine gave just as good results as 

 when the elaborate method of gradual replacement by the use of 

 chloroform was resorted to. The final imbedding took place in 

 pure hard paratfine of G0° C. melting point. 



In spite of the siliceous spicules very thin sections can be 



