906 SUMMARY or CURRENT RESEARCHES RELATING TO 



previously injected thin mass before it until the plaster has reached 

 the capillaries, where its onward movement is arrested. Prof. 0. P. 

 Hay uses the following method, based on the same principle. 



A canula is fitted into the aorta of a cat, and a gelatin mass 

 coloured with carmine injected until it is seen to flow from the right 

 side of the heart ; then the tube conveying the red mass being detached, 

 a tube conveying a blue gelatin mass is slipped over the same canula, 

 and the pressure again applied. Into this blue mass had been mixed 

 thoroughly a quantity of starch, preferably from wheat. This starch- 

 bearing mass pushes the carmine mass before it until the starch-grains 

 enter the capillaries and effectually plug them up. The arteries are 

 thus left blue and the veins red, and so well is the work accomplished* 

 that a lens of considerable power must be used to discover any admix- 

 ture of the colours in the smallest vessels of thin membranes. 



Double Injections for Histological Purposes.* — Prof. 0. P. Hay 

 refers to the usual method of producing a double injection of the 

 blood-vessels preparatory to making sections for the Microscope, by 

 injecting first a gelatin mass of one colour into the artery until the 

 increasing pressure gives notice that the mass is entering the capil- 

 laries, and immediately after to inject a differently coloured mass into 

 the vein. The injection being thus accomplished, one of two things, 

 it seems to him, is likely to happen ; either the vessels will not be 

 well filled, or the mass intended for one set of vessels will be driven 

 through into the other. 



To avoid these accidents he has practised the method of filling 

 both sets of vessels at the same moment and under exactly the same 

 pressure. This pressure is kept low at the beginning, so that all the 

 arteries and veins shall be thoroughly filled before either mass begins 

 to enter the capillaries. Then as the pressure is increased the 

 differently coloured masses meet each other in the capillaries ; and 

 if the pressure on each is equal, the vessels may be filled as full 

 as compatible with safety, without danger of either colour being 

 driven from one set of vessels into the other. The desired pressure 

 is secured by allowing a stream of water from a hydrant or cistern to 

 flow into a tight vessel. As the water flows in, the air is forced out 

 through a rubber tube A (fig. 218) into the wide- mouthed bottle F, 

 whose tightly fitting cork gives passage to two other glass tubes. 

 These extend below just through the cork, and above connect respec- 

 tively with the rubber tubes C and D. Into the side of F near the 

 bottom is fitted another tube E, reaching to a height of ten inches or 

 more, open above, and graduated into inches. If preferred, this tube 

 may also pass through the cork, and extend down well into the mer- 

 cury with which F is partly filled. B is a bottle of suitable size in 

 which is contained a blue injection-mass for filling the veins, and R 

 a similar bottle containing a red mass for the arteries. The interiors 

 of these bottles are connected with the bottle F by the tubes D and C. 

 Each of the bottles B and E has a tube which, starting from near the 

 bottom, passes through the cork, and is, a little above this, bent at 



* Amer. Natural., xix. (1885) pp. 527-9 (1 fig.). 



