•24 
Argas persicus 
that faithful preservation of histological detail is not a sine qua non, the 
classic Kleinenberg’s picro-sulphuric acid fixative, used undiluted and 
hot, gives good results. After fixing, every trace of the fixing reagent 
must be eliminated from the tissues, prior to embedding in paraffin. 
Perfect dehydration is essential to successful embedding, and the 
absolute alcohol-chloroform-parafifin sequence—the Senkviethode of 
F. E. Schulze^—has proved of admirable service in the hands of the 
authors. Hard paraffin with a melting-point of 58° C.-60° C. should be 
used, and the duration of the paraffin bath must not be prolonged for 
a moment more than is absolutely necessary. If the vacuum method of 
embedding can be applied, the time required for thorough penetration 
by the paraffin is very materially reduced. A little ingenuity will 
suggest a method by means of which an ordinary mechanical air-pump, 
such as is available in most laboratories, can be utilised for the purpose, 
and the results will prove to be as good as those obtained by the use of 
the expensive, vacuum-embedding baths which are advertised in the 
instrument-makers’ catalogues. 
Tick material, prepared by the methods described above, wull cut 
perfectly on a microtome of the Minot pattern, without displacement or 
fracture of the chitinous parts. A thickness of 10 yu. is most suitable 
for general purposes. It is perhaps unnecessary to observe that the 
microtome knife should be in perfect condition to ensure successful 
results. 
Tlie authors have tried the collodion-method of embedding, but 
the results were far from satisfactory. With proper care, the paraffin 
method yields results which are all that can be desired. 
The preparation of material for the study of the histological details 
of the internal organs involves more care. Kleinenberg’s fixative is 
quite unsuitable; Carnoy’s fluid, Flemming’s fluid, or others which give 
a satisfactory fixation of the soft tissues must be used. It has been 
found necessary to aid the penetration of these fluids by the use of 
an injecting syringe, in the manner advocated by Nordenskibldv The 
description of these special methods will, however, be more conveniently 
dealt with in connection with the internal anatomy. 
1 Eawitz, B., Leitfaden fiir Instiologische Untersuclmngen, Yerl. Gustav Fischer, Jena, 
1895, p. 33. 
- Nordenskiolcl, E. (1908). 
