ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 739 



accurately of the condition of tlie surface of the paraffin, which 

 reflects the light. Everything being in readiness, the brush is 

 lifted and wiped on the mouth of the bottle to remove most of the 

 collodion, and then the paraffin and the object are at once painted by 

 quickly drawing the brush across the surface, care being used that it is 

 evenly applied and that the collodion is not carried on to the vertical 

 faces of the block. The temporary moistening vanishes like a cloud 

 from the surface of the paraffin ; the brush is then returned to the 

 bottle; the knife is drawn and returned, leaving the section on the 

 edge of the blade. The object in the block is then painted again, 

 but before drawing the knife a second time the first section is re- 

 moved with a scalpel and placed on the slide with its upper face in 

 contact tcith the fixative. Then the knife is drawn again, and the 

 other steps of the process repeated. Thus the collodion has time to 

 dry thoroughly before the section is made. If the precautions 

 above given are observed it will not be necessary to wait for the 

 drying of the collodion, but the section may be cut at once, i. e. 

 within five seconds after painting. It is thus possible to cut as 

 fast as one can paint the surface, and with some practice it becomes 

 possible to cut continuous ribbons of sections, which may be trans- 

 ferred at intervals. Practically I find it most convenient to cut 

 enough to form one row or half a row of sections at a time and 

 transfer at once to the slide, rather than to cut the whole object 

 without interruption, as is done in the ordinary method. 



The following precaution may prove serviceable : — Especial care 

 should be exercised to prevent the painting of the vertical face nearest 

 the operator, since the section is then liable to cling along its whole 

 edge to this vertical film and be carried under the knife-blade. If by 

 chance this should occur, the section should be removed from the 

 block before the knife is moved back, as it is liable to be caught and 

 lacerated between the face of the block and the under surface of the 

 returning blade. The possibility of the section being thrown under 

 the knife-blade may, however, be obviated either by carefully trim- 

 ming the vertical face in case it is accidentally painted (to allow of 

 which the hither margin of the paraffin may be left broader than the 

 other three), or by drawing the knife sloivly, so that the first indica- 

 tion of a failure to cut through the vertical film may be recognized 

 and the section held in place on the blade by a slight pressure with 

 a soft brush, whereupon the knife will cut through the film and 

 leave the section free. 



If by chance the paraffin block has been painted with too much 

 collodion or with collodion which is too concentrated, thus leaving a 

 shiny surface, the film sliould be at once broken by pressing it gently 

 two or three times in quick succession with the end of a rather stiff, 

 blunt, dry brush. This enables the collodion to dry quickly, and 

 thus prevents the softening of the paraffin. 



If the sections have a tendency to curl they may be flattened out 

 on the slide by means of a bruslijfor a section thus impregnated with 

 wjllodion may be handled during the first few seconds after contact 

 with the Bchiillibaurn mixture with much greater impunity than one 



