Walter Gardixer. 
58 
of difficulty, for if it Ito allowed to aet for too short a time the cell- 
wall will not be sufficienllv swollen, wliile if tho treatinont be somewhat 
prolonged, the middle lamellae of the colls are liable to sw eil, and at the 
same time stain, and, whcn in such a condition, will liinder all successful 
observation of the threads which may traverso their substance. Upon still 
further action the proloplasm ilself commences to be attacked. With Ghlor- 
Zinc-Jod. on the other hand, whore the action is much moro regulalcd and 
gradual, but littlo precaution as to length of time need be observed. 
Besides the difficulty of regulating ils action, liiere are still other and 
grave objections to the use of Sulphuric acid. One of these is that no matter 
hovv carefully the acid is added to the tissue, and no matter how quickly 
the washing in water is accomplished, there will be a very considerable 
evolulion of heat attending the hydralion of tho acid, which is liable to ac- 
celcrate ils action and to cause very grave changes in such dclicate struc- 
tures as fine protoplasmic filaments traversing the cell-wall. Secondly the 
folding up and general displacement of the tissue consequenl uj>on the 
action of such a violent roagent, greatly increases the already exisling com- 
plications which attend all observations connected with minute hislology. 
For these reasons, wliile 1 still regard Sulphuric acid as a very valuable 
reagent, bolh for swelling up resistent tissues upon which Ghlor-Zinc-Jod. 
has luil littlo action, and for demonstraling in an unusually clear wav the 
remarkable manner in which the apices of the protoplasmic proccsses, 
entering the pits, ding to the pit-closing-membrane, yet 1 am convinced that 
il must be looked upon as the less satisfactory of the tvvo, and that the 
phenomena produced in consequence of its action can only be rightly iuter- 
preled in the light of the more certain results oblained by the use of Chlor- 
Zinc-Jod. Finally I am of opinion that for all tissues which will sw eil suffi- 
cientlv under its action, my Ghlor-Zinc-Jod. method may be regarded as 
perfcctly satisfactory, and that aller troatment with Picric-lloFKMAiNN’s- 
blue and subsequent washing in water, nothing but protoplasmic structures 
will bc stained. In clear inslances whore a thick closing-membrane is 
plainly traversed by threads, it can be demonstrated with easc that while 
tho individual threads are well stained, the substance of the pit-membrane 
ilself experienccs no colouration, eveu whcn the seelion has been exposed 
to the action of the dye for a long time. When the pits are smaller and the 
threads less clearly defined it is more difficult to observe that the substance 
of the pit-membrane is still free from colouration, and whcn owing to the 
thinness of tho closing-membrane, all appearances even of striation cease 
to be reeognizable, wo are only aI> 1 o to observe an apparent staining of the 
enlire membrane. But 1 am convinced from my own tentative experiment, 
and I Ihink anyone who follows this paper to the end, w ill bc convinced also 
that such staining points not to the colouration of the substance of the pit-mem¬ 
brane, but to the staining of protoplasmic filaments traversing its slruclure. 
