116 APPENDIX TO THE HISTOLOGICAL SECTION. 



4. After this period the muscles may be removed with a spoon. 

 They will be found practically free of fat and connective tissue, and 

 only loosely attached, but in their original relationship. They can now 

 be detached with a spatula from the bone, and be isolated by 

 teasing or pressure. The fibres are coagulated and tough. By careful 

 separation in dilute glycerine the fibres can be completely isolated and 

 measured. 



Injection of blood vessels With coloured gelatin masses. 



As this is an operation which the student is ordinarily not required 

 to perform himself, a sketch of the process will suffice. Access to the 

 blood vascular system is gained by exposing the heart of an animal 

 with the least injury to the surrounding parts, in order to guard against 

 the escape of injection through accidentally injured blood vessels. 

 The apex of the heart is cut off and the blood allowed to escape. 

 A glass cannula or nozzle is secured in the aorta, and is connected 

 with the injecting apparatus. A ligature is disposed around the ven- 

 tricles ready for closure in order to control the venous outlet. In 

 the case of a single organ the cannula is secured in the chief artery 

 and bull-nosed artery forceps are used to control leakages and the 

 venous channels. The injection apparatus is a brass syringe or an 

 appliance acting under continuous air pressure. When all parts of 

 the object appear injected the venous outlet is closed, the pressure 

 is maintained a little longer and the aorta is clamped to confine the 

 injection. During the injection avoid the introduction of air with the 

 fluid, arrest leakage from injured blood vessels, and use the lowest 

 pressure that will suffice to drive the fluid through the capillaries 

 the occurrence of which can be recognised by the change of colour in the 

 tongue, nose, eyes, &c. The gelatine mass is then set by immersing 

 the object in cold alcohol, after which the parts required are cut into 

 suitable pieces and hardened in spirit. 



Blue gelatin mass. Take 25 parts of a saturated solution of soluble 

 Berlin blue (Brucke's blue), 1 warm it and to it add slowly, with 

 constant stirring, 1 part of the best French gelatin, which has been 

 allowed to swell in distilled water, and has then been melted by 

 heating in the water which it has imbibed. When thoroughly incor- 

 porated filter the mixture through flannel wrung out of hot water ; it 

 is then ready for use. Injected parts gain by being preserved at 

 first in Miiller's fluid or 2 P- C - bichromate of ammonia the colour of the 

 mass is thereby greatly improved (Ranvier). After staining in bulk 

 with borax carmine cut by freezing in paraffin. 



1 Can be obtained from Dr. Griibler, through Kauthack, 18, Berner's Street, 

 London, W. 



