o4 Answers to Quertes. 
the slides on a hot-water cistern, in front of the fire, or where the 
temperature is decidedly higher than the ordinary temperature of 
the air. In no case will the balsam become perfectly hard under 
the. centre of the cover, unless the slide be heated considerably, 
but it gradually hardens pretty well round the margin, if not 
hurried, although in the middle it keeps softer in proportion. The 
less superfluous balsam there is round the edge of the cover the 
more rapid will be the drying. I may mention that most mounters 
invariably use benzole asa solvent for balsam, despite its cloudy 
ways. G. HSB: 
332.—Blood-Corpuscles.—Colourless blood-corpuscles have 
lately been discovered to have a supremely useful function in the 
animal system. They devour substances which have become 
useless in the system, and they wage war upon substances foreign 
to the system, In transparent skinned animals the process has 
absolutely been observed, by which the white blood-corpuscles, or 
** leucocytes,” attack and devour the bacilli of anthrax ; or, as in 
the case of absorption of the tales of tadpoles, are seen hurrying 
along in the circulation, loaded with the muscular débris they 
have devoured. When the leucocytes can easily overcome and 
devour any special bacilli, these bacilli are not harmful to the 
animal in question ; where the leucocytes have a hard struggle the 
bacilli are dangerous; when the leucocytes are defeated, the 
disease is deadly. Most interesting accounts of the experiments 
on this subject will be found in Mr. Blend Sutton’s /x¢roduction to 
General Pathology, and an account intended for non-medical read- 
ers has been published in the Journal of Microscopy and Natural 
Science, for January, 1888, under the heading of ‘ Micro-Organ- 
isms as Parasites.” It is supposed, on good grounds, that the 
white blood-corpuscles are actively engaged in the production of 
the red blood-corpuscles, and that the process takes place in the 
“red marrow” of the bones, the spleen, and the thyroid gland. 
The leucocytes are developed from the endothelial layer of the 
body, which in very primitive organisms (such as the sponges, etc.) 
are engaged throughout life in devouring substances for the benefit 
of the community, whilst other cells propel the body, or keep up 
currents of water. In the highest animals, the leucocytes are 
still true to their original function, and are sometimes distinctively 
known as phagocytes. I am not aware of any difference, 
physiological or chemical, between the white corpuscles and 
ordinary amcebze. Haéckel purposely places drawings of the two 
side by side, in order to show their absolute likeness. Leucocytes 
do not ordinarily, like free amcebz, emit pseudopodia; they are 
carried along fast enough by the free current of the blood, but 
they can under certain circumstances, move and emit pseudopodia, 
precisely like amcebe, and they feed in the same manner, 
