lly, for the purposes of office classification, to
state a _peculiar property_ (not an accident) of the objects included in
the class; and to define a species under the class it is sufficient to
state the name of the class plus the difference--i. e., with the
addition of the limitations that characterize the species.[11] This
procedure in definition is susceptible of application from the highest
genus to the lowest species. It is advisable to define the means
included within a title without any introductory words, such as "this
subclass includes inventions relating to," etc., treating the subclass
for definition purposes as if it were a collection of concrete things,
in the same manner as in a dictionary definition.

CROSS-REFERENCES AND SEARCH-NOTES.[12]

If patents were in all respects like material objects, cross-references
and search-notes would not be necessary. Nails, screws, locks, hinges,
and boxes are distinct things susceptible of definite separation and
classification. Even though nails, screws, locks, and hinges form part
of the box, the box is still a box, not a nail, screw, hinge, or lock.
For the needs of the Patent Office classification, however, although a
patent for a box must be classified with boxes, yet if a peculiar nail,
screw, lock, or hinge is claimed in the same patent with the box, or
even if any one of these customary accessories of boxes is illustrated,
it may be necessary to provide copies of the patent for the box in each
of the several classes provided for nails, screws, locks, or hinges.

Inasmuch as every relatively complex thing is made up of relatively
simple things, it is obvious that all disclosures can not be
cross-referenced. Any attempt to calculate the number of
cross-references to be supplied if all disclosures of the subjects of
invention were to be cross-referenced would show the number to be
incalculable. It is necessary, therefore, to leave to the judgment of
the classifier the propriety of cross-referencing unclaimed disclosures.

Should a patent contain a number of claims defining a number of
differently classifiable inventions, complete cross-referencing from the
class in which the classification is made original into the other
appropriate classes or subclasses should be effected, _unless_
cross-search notes or arrangement of subclasses with appropriate titles
may be substituted to advantage.

Cross-referencing or cross-search notes are made, as a rule, from
combi