STUDIES IN THE EXl'EKIMENTAE ANALYSIS OF SEX. 269 
combination of two kinds of dye, one the original basic oxazine 
dye which unites with fatty acid to form a blue compound, and 
the other a derivative of the base, a red oxazone not basic in 
character, but soluble in liquid fat and giving it a red colour.’^ 
In Weigert’s bichromate hasrnatoxylin method sections pre- 
served in formalin and cut on the freezing microtome are 
subjected to the action of saturated potassium bichromate for 
periods varying from 12-120 hours at a temperature of about 
37^ C. They are then washed and stained in hminatoxylin 
overnight and subsequently differentiated in Weigert’s borax 
ferricyanide solution. 
The staining of the fat or lipoid by the haematoxylin 
depends on the formation of a compound of the fat with 
chromium oxide which forms a lake with the haematoxylin* 
This compound is, however, only formed by fats in which an 
unsaturated groupingof the component atoms occurs, and the 
more of such unsaturated groupings are present the quicker 
does the bichromate form the compound which is stained by 
the haematoxylin. The length of time, therefore, that the 
sections have to remain in the bichromate is a measure of the 
degree to which the fats or lipoids present are saturated or 
nn saturated. 
The employment of the Nile blue sulphate method has given 
results of more importance for oiir inquiry than the Weigert 
method. 
W e may consider first the proof that the ova of the nortnal 
female crab in the course of becoming ripe take up fat from 
the blood, first of all in the form of neutral fat-globules, and 
then convert them into yolk-globules with a different staining 
reaction. 
Sections of a practically mature yellow or dark pink ovary 
stained with the Nile Blue rnetliod will show principally ripe 
eggs containing large yolk-globules which are stained purple. 
A small cytoplasmic zone round the nucleus is stained blue;, 
the nucleus is colourless except for a very dark blue nucleolus. 
In a less ripe ovary eggs are seen which, in addition to the 
purple staining yolk-globules, contain mnch smaller globnles 
