388 
DE. M. TONGE ON THE DEVELOPMENT OE THE SEMILUNAE 
liar mode of preparation of the embryo, I will first give a brief account of the method I 
followed successfully. It was obvious that these tissues being from the first highly 
elastic, and also contractile, would collapse immediately the circulation stopped, and in 
this collapsed condition it would be impossible to examine the anatomy of the interior 
of the vessel with any degree of certainty, the difficulty being enhanced by the softness 
of the tissues in their natural state. It seemed to me that this was the point where 
former investigators must have failed. The desideratum was to obtain the large vessels 
in a distended and hardened state, and at the same time transparent and fit for exami- 
nation by transmitted light. To effect this the embryo immediately on its removal from 
the egg was immersed in strong spirit of wine, the sac of the amnion being first slit 
open, where this had closed up, in order that the spirit might come freely into contact 
with every part of the surface of the embryo. As the spirit permeates the tissues of the 
embryo, which it does rapidly, the capillaries and smaller vessels are soonest contracted 
by it, and the blood being thus prevented from escaping from the larger arteries before 
the heart’s action is stopped, they become greatly distended. When this distension with 
blood reaches its maximum in the arteries, the blood accumulates in the cavities of the 
heart and in the large veins, the impediment caused by the closure of the systemic 
capillaries and small arteries acting backwards throughout the circulation. By this 
treatment it was found that the cavities of the heart, and the large vessels nearest to the 
heart, became fully distended with blood, and becoming coagulated and hardened by the 
spirit retained the distended condition. The embryos were allowed to remain in the 
alcohol for a few hours or days, according to their size, in order that they might become 
completely hardened. By careful management of the position of the embryo in the 
corked glass tube, I was frequently able to obtain a colourless clot in the large vessels, 
owing to the sinking of the corpuscles before the blood had coagulated or the spirit had 
penetrated the walls of the artery. The best position for obtaining this result was to 
keep the head of the embryo downwards, and the body a little inclined towards its dorsal 
surface. The embryos after being hardened in spirit were of course perfectly opaque, 
and could only be examined by reflected light till they had been rendered transparent. 
This was effected by soaking them in strong Price’s glycerine for several days. After 
this the portions required for examination were removed, and dissected and examined in 
glycerine by strong transmitted light under a compound microscope fitted with an erector 
and a low power (1 inch). The hardness of the tissues permitted sections to be made 
readily in various planes, and their transparency under strong light enabled the 
course of the vessels distended with coagulated blood to be readily followed. Where it 
was required to examine the structure of the interior of the cavities of the heart and 
great vessels the coagula, if opaque, were first carefully picked out by needles : if a 
colourless coagulum had been obtained this troublesome process was often unnecessary. 
After dissection in strong glycerine the specimens were mounted for drawing and 
description. They were preserved in glycerine jelly, this medium retaining the specimen 
in any position in which it was required to be drawn or described, and allowing of its 
