148 
IOWA ACADEMY OF SCIENCES. 
First — It does not extract water from the tissues and conse- 
quently it does not shrink them. The distortion of an animal 
will be in direct proportion to the shrinkage of its tissues, and 
this, in turn to the amount of water extracted. Hence it was 
that our attempts to preserve such watery forms as medusae, 
ctenophores, etc., with our old media were always failures; our 
preserving fluids dehydrated them. Formaldehyde, however, 
will preserve almost every form of animal life known without 
any distortion. Such a fact opens up possibilities for class 
instruction which are almost ideal. 
Second . — Most of the pigments of the animal body are not 
extracted by formaldehyde. This quality ranks next in impor- 
tance to the preceding one. Natural coloration enters so largely 
into our conceptions of animals that bleaching during the pro- 
cess of preservation is always to be deplored. With alcohol as 
the preserving fluid, all parts are certain to be brought to the 
same level of dingy yellow after a time. But with formalde- 
hyde, we can hope to show our students the colors which 
actually characterized the animals during life. 
Third . — It does not render tissues opaque. On the contrary 
it retains the transparency of the living parts, or may even add 
to it. Nerves are aften more readily traced after preservation 
than during life. 
Fourth . — It leaves tissues as flexible as it is possible for them 
to be. The natural elasticity of the parts is usually perfectly 
retained, and brittleness never occurs. 
Fifth . — It is a very convenient reagent for collectors to use. 
The preserving medium is a dilute solution of the commercial 
article in water. A collector can carry enough formaldehyde 
in a bottle -which will slip into his coat pocket to make several 
gallons of the preservative. The water used in diluting it 
should always be that from which the collection is made, either 
salt or fresh, as the case may be. 
Sixth.— li is a very cheap reagent. The commercial article 
is imported duty free by the State University of Iowa in 100- 
pound lots at a cost of 40 cents per pound. When made up in 
a 4 per cent solution the cost of a gallon is thus only 12 4-5 
cents. 
We might, in fact, summarize the various desirable qualities 
of formaldehyde as a preserving medium as being ‘ ‘ very close 
to the ideal.” A reagent which preserves faithfully all natural 
features just as they were during life. That it is infinitely 
