626 General Notes. [June, 
the greater length of the dasis cranii. It may not be premature 
therefore to say that the species homo sapiens is divided into three 
sub-species as follows : 
Microdont subspecies. 
Mesodont subspecies, 
Megadont subspecies, 
e may then reserve the term race for those actual grand 
divisions of humanity, twelve or fifteen or more, as the case may 
be, resulting from the crossing of these sub-species. 
MICROSCOPY:! . 
THE Uses oF CorLonion.—In modern histological technique 
collodion has come to serve a variety of important purposes. 
Duval? was the first to call attention to its advantages as an im- 
bedding mass. He found that it penetrated preparations easily and 
thoroughly ; that it could be quickly brought to the proper degree 
of hardness in alcohol of 36° (80 %); that objects thus imbedded 
could be preserved in this alcohol for an indefinite length of time; 
that the imbedding mass preserved its transparency, so that the 
preparation could be easily examined; that the sections did not 
require to be freed from the mass, since they could be colored 
and mounted in glycerine, and the mass remain unaffected by the 
process. 
As soon as Duvgl’s discovery became known, Merkel and 
Schiefferdecker’ began to experiment with collodion, and greatly 
improved and extended its use. 
It was found desirable first of all to be able to vary the concen- 
tration of the collodion, an end very conveniently reached by 
Merkel through the use of a solid preparation, called cel/oidin, 
which he dissolved in absolute alcohol and ether in equal parts. 
uval mounted sections of objects imbedded in collodion in 
glycerine, and was unsuccessful in his experiments with balsam. 
95 per cent alcohol, and clarifying in oil origanum or oil of ber- 
gamot, the sections could be mounted in balsam (“ Microscopy,” 
Aug., 1884, p. 843). 
Some improvements of minor importance in the process of im- 
bedding have been made by Thoma, Blochmann and others. 
e importance of collodion in microtomy was much increased 
by the discovery that in combination with clove oil it could be 
1 Edited by Dr. C. O. WHITMAN, Mus. Comparative Zoology, Cambridge, Mass. 
Nie Joem- de V'anat, et de la physiol., xv, p. 185, 1879. 
nee Arch. f. Anat. u. Physiol., Anat, Abth., p. 199, 1882. 
coe * Arch, f. mik, Anat., XXII, p. 689, 1883. 
